Simplified tectonic map of Mount Etna, modified after 

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... about 4:00 GMT on 27 October, a third fissure opened along the NE-Rift. This fissure was 3.7 km long and trended SW-NE (Figs. 2, 4). It propagated between 2500 m and 1890 m a.s.l. in less than 24 h. In Fig. 3 we show segment 3a between 2500 and 2300 m a.s.l., observations, which revealed low-level strombolian ac- trending N20–30E, that was 1.2 km long and showed tivity inside the crater. Strombolian activity at this crater violent strombolian activity. Segments 3b+3c of the fis- increased in July, leading to fallout of bombs on the sure, 0.7 km long and trending N30–45E, formed in a crater’s outer flanks. The erupted products were por- right en-echelon arrangement between 2290 and 2190 m phyritic (phenocrysts made up 25% of the total volume) a.s.l., producing fire fountaining and effusive activity. trachybasalts with their mineral assemblage dominated Lava effusion produced a 1 km-long flow from a vent at by plagioclase. These features are typical of volcanics 2500 m a.s.l. During the down-slope propagation of the produced by summit craters over the past 10 years fissure system a series of pit craters formed along the (Corsaro and Pompilio 2004a, 2004b). During this whole upper segments and the first, upper lava flow became period, the SEC remained quiescent, with its conduit inactive. Meanwhile, a second flow emerged from a vent obstructed, whilst Voragine (VOR; Fig. 3) showed pre- at 2200 m a.s.l. flowing east and partially submerging the dominantly quiescent degassing. Piano Provenzana tourist infrastructure (Figs. 4, 6a). A On 22 September 2002, an earthquake (Md=3.7, fo- shallow seismic swarm associated with the fissure prop- cal depth=5 km; Acocella et al. 2003), accompanied by agation seriously damaged all of the tourist-hotel facilities surface fracturing, occurred along the PFS (Fig. 1). This on Piano Provenzana. The earthquakes caused movements earthquake strongly remobilised the PFS after about along the whole PFS (~18 km) and up the Ionian coast 15 years of quasi-quiescence, marking the beginning of an (Acocella et al. 2003; Neri et al. 2004). On the early important displacement of the eastern flank of Etna. A morning of 28 October, the northern eruptive fissure survey on the summit of the volcano carried out imme- (N45–65E) propagated down-slope for 1.8 km to 1890 m a.s.l. The lower segment (3d, Fig. 3) of the fracture At about 4:00 GMT on 27 October, a third fissure opened along the NE-Rift. This fissure was 3.7 km long and trended SW-NE (Figs. 2, 4). It propagated between 2500 m and 1890 m a.s.l. in less than 24 h. In Fig. 3 we show segment 3a between 2500 and 2300 m a.s.l., trending N20–30E, that was 1.2 km long and showed violent strombolian activity. Segments 3b+3c of the fissure, 0.7 km long and trending N30–45E, formed in a right en-echelon arrangement between 2290 and 2190 m a.s.l., producing fire fountaining and effusive activity. Lava effusion produced a 1 km-long flow from a vent at 2500 m a.s.l. During the down-slope propagation of the fissure system a series of pit craters formed along the upper segments and the first, upper lava flow became inactive. Meanwhile, a second flow emerged from a vent at 2200 m a.s.l. flowing east and partially submerging the Piano Provenzana tourist infrastructure (Figs. 4, 6a). A shallow seismic swarm associated with the fissure propagation seriously damaged all of the tourist-hotel facilities on Piano Provenzana. The earthquakes caused movements along the whole PFS (~18 km) and up the Ionian coast (Acocella et al. 2003; Neri et al. 2004). On the early morning of 28 October, the northern eruptive fissure (N45–65E) propagated down-slope for 1.8 km to 1890 m a.s.l. The lower segment (3d, Fig. 3) of the fracture (~1 km long) showed continuous strombolian activity and a lava flow directed NE (Fig. 4), that travelled a distance of ~2.5 km (Fig. 6b) in a few hours. On 29 October, a NW-SE tectonic structure (SV in Fig. 1) located on the lower eastern flank of the volcano was activated by seismic swarms of 4.4 maximum mag- nitude that caused serious damage to houses and infrastructure around S. Venerina (SV in Fig. 1; Acocella et al. 2003). During the same day, the NE lava flow slowed and a new lava flow erupted from the same fissure (seg- ment 3d in Fig. 3) at 1930 m a.s.l., flowing SE and in- vading Piano Provenzana. The NE flow (Fig. 4) stopped on 31 October after having travelled 2.8 km, when a decline in effusion rate was observed. The explosive activity began to decrease slowly from 29 October and on 1 November it was limited to just two vents on the lower portion of the fissure, between 1950 and 1900 m a.s.l. This indicated a general waning of the eruptive activity on this side of the volcano. The eruptive plume did not exceed an altitude of 1 km above the vents, and fallout affected only the nearby areas. Strombolian activity formed two coalescent spatter cones at 1950–1900 m a.s.l. The E lava flow reached a final length of 6.2 km, and stopped its expansion on 3 November (Fig. 4). After lava supply from the main vent was cut off, 20 m of down- slope movement was observed at the most advanced flow front on 5 November. This late movement was caused by channel emptying, and occurred when lava coming from the main vent was completely crusted over. The ski station and tourist shops on Piano Provenzana were first destroyed by earthquakes then partially covered by lava flows. The flows also caused fires and destroyed parts of the old Linguaglossa pine forest (Fig. 4). Explosive and effusive activity completely stopped at the north fissure on 5 November. The morphology of the lava flows was “aa” in type, and the longer flows showed formation of wide ...

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... about 4:00 GMT on 27 October, a third fissure opened along the NE-Rift. This fissure was 3.7 km long and trended SW-NE (Figs. 2, 4). It propagated between 2500 m and 1890 m a.s.l. in less than 24 h. In Fig. 3 we show segment 3a between 2500 and 2300 m a.s.l., observations, which revealed low-level strombolian ac- trending N20–30E, that was 1.2 km long and showed tivity inside the crater. Strombolian activity at this crater violent strombolian activity. Segments 3b+3c of the fis- increased in July, leading to fallout of bombs on the sure, 0.7 km long and trending N30–45E, formed in a crater’s outer flanks. The erupted products were por- right en-echelon arrangement between 2290 and 2190 m phyritic (phenocrysts made up 25% of the total volume) a.s.l., producing fire fountaining and effusive activity. trachybasalts with their mineral assemblage dominated Lava effusion produced a 1 km-long flow from a vent at by plagioclase. These features are typical of volcanics 2500 m a.s.l. During the down-slope propagation of the produced by summit craters over the past 10 years fissure system a series of pit craters formed along the (Corsaro and Pompilio 2004a, 2004b). During this whole upper segments and the first, upper lava flow became period, the SEC remained quiescent, with its conduit inactive. Meanwhile, a second flow emerged from a vent obstructed, whilst Voragine (VOR; Fig. 3) showed pre- at 2200 m a.s.l. flowing east and partially submerging the dominantly quiescent degassing. Piano Provenzana tourist infrastructure (Figs. 4, 6a). A On 22 September 2002, an earthquake (Md=3.7, fo- shallow seismic swarm associated with the fissure prop- cal depth=5 km; Acocella et al. 2003), accompanied by agation seriously damaged all of the tourist-hotel facilities surface fracturing, occurred along the PFS (Fig. 1). This on Piano Provenzana. The earthquakes caused movements earthquake strongly remobilised the PFS after about along the whole PFS (~18 km) and up the Ionian coast 15 years of quasi-quiescence, marking the beginning of an (Acocella et al. 2003; Neri et al. 2004). On the early important displacement of the eastern flank of Etna. A morning of 28 October, the northern eruptive fissure survey on the summit of the volcano carried out imme- (N45–65E) propagated down-slope for 1.8 km to 1890 m a.s.l. The lower segment (3d, Fig. 3) of the fracture At about 4:00 GMT on 27 October, a third fissure opened along the NE-Rift. This fissure was 3.7 km long and trended SW-NE (Figs. 2, 4). It propagated between 2500 m and 1890 m a.s.l. in less than 24 h. In Fig. 3 we show segment 3a between 2500 and 2300 m a.s.l., trending N20–30E, that was 1.2 km long and showed violent strombolian activity. Segments 3b+3c of the fissure, 0.7 km long and trending N30–45E, formed in a right en-echelon arrangement between 2290 and 2190 m a.s.l., producing fire fountaining and effusive activity. Lava effusion produced a 1 km-long flow from a vent at 2500 m a.s.l. During the down-slope propagation of the fissure system a series of pit craters formed along the upper segments and the first, upper lava flow became inactive. Meanwhile, a second flow emerged from a vent at 2200 m a.s.l. flowing east and partially submerging the Piano Provenzana tourist infrastructure (Figs. 4, 6a). A shallow seismic swarm associated with the fissure propagation seriously damaged all of the tourist-hotel facilities on Piano Provenzana. The earthquakes caused movements along the whole PFS (~18 km) and up the Ionian coast (Acocella et al. 2003; Neri et al. 2004). On the early morning of 28 October, the northern eruptive fissure (N45–65E) propagated down-slope for 1.8 km to 1890 m a.s.l. The lower segment (3d, Fig. 3) of the fracture (~1 km long) showed continuous strombolian activity and a lava flow directed NE (Fig. 4), that travelled a distance of ~2.5 km (Fig. 6b) in a few hours. On 29 October, a NW-SE tectonic structure (SV in Fig. 1) located on the lower eastern flank of the volcano was activated by seismic swarms of 4.4 maximum mag- nitude that caused serious damage to houses and infrastructure around S. Venerina (SV in Fig. 1; Acocella et al. 2003). During the same day, the NE lava flow slowed and a new lava flow erupted from the same fissure (seg- ment 3d in Fig. 3) at 1930 m a.s.l., flowing SE and in- vading Piano Provenzana. The NE flow (Fig. 4) stopped on 31 October after having travelled 2.8 km, when a decline in effusion rate was observed. The explosive activity began to decrease slowly from 29 October and on 1 November it was limited to just two vents on the lower portion of the fissure, between 1950 and 1900 m a.s.l. This indicated a general waning of the eruptive activity on this side of the volcano. The eruptive plume did not exceed an altitude of 1 km above the vents, and fallout affected only the nearby areas. Strombolian activity formed two coalescent spatter cones at 1950–1900 m a.s.l. The E lava flow reached a final length of 6.2 km, and stopped its expansion on 3 November (Fig. 4). After lava supply from the main vent was cut off, 20 m of down- slope movement was observed at the most advanced flow front on 5 November. This late movement was caused by channel emptying, and occurred when lava coming from the main vent was completely crusted over. The ski station and tourist shops on Piano Provenzana were first destroyed by earthquakes then partially covered by lava flows. The flows also caused fires and destroyed parts of the old Linguaglossa pine forest (Fig. 4). Explosive and effusive activity completely stopped at the north fissure on 5 November. The morphology of the lava flows was “aa” in type, and the longer flows showed formation of wide ...

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... about 4:00 GMT on 27 October, a third fissure opened along the NE-Rift. This fissure was 3.7 km long and trended SW-NE (Figs. 2, 4). It propagated between 2500 m and 1890 m a.s.l. in less than 24 h. In Fig. 3 we show segment 3a between 2500 and 2300 m a.s.l., observations, which revealed low-level strombolian ac- trending N20–30E, that was 1.2 km long and showed tivity inside the crater. Strombolian activity at this crater violent strombolian activity. Segments 3b+3c of the fis- increased in July, leading to fallout of bombs on the sure, 0.7 km long and trending N30–45E, formed in a crater’s outer flanks. The erupted products were por- right en-echelon arrangement between 2290 and 2190 m phyritic (phenocrysts made up 25% of the total volume) a.s.l., producing fire fountaining and effusive activity. trachybasalts with their mineral assemblage dominated Lava effusion produced a 1 km-long flow from a vent at by plagioclase. These features are typical of volcanics 2500 m a.s.l. During the down-slope propagation of the produced by summit craters over the past 10 years fissure system a series of pit craters formed along the (Corsaro and Pompilio 2004a, 2004b). During this whole upper segments and the first, upper lava flow became period, the SEC remained quiescent, with its conduit inactive. Meanwhile, a second flow emerged from a vent obstructed, whilst Voragine (VOR; Fig. 3) showed pre- at 2200 m a.s.l. flowing east and partially submerging the dominantly quiescent degassing. Piano Provenzana tourist infrastructure (Figs. 4, 6a). A On 22 September 2002, an earthquake (Md=3.7, fo- shallow seismic swarm associated with the fissure prop- cal depth=5 km; Acocella et al. 2003), accompanied by agation seriously damaged all of the tourist-hotel facilities surface fracturing, occurred along the PFS (Fig. 1). This on Piano Provenzana. The earthquakes caused movements earthquake strongly remobilised the PFS after about along the whole PFS (~18 km) and up the Ionian coast 15 years of quasi-quiescence, marking the beginning of an (Acocella et al. 2003; Neri et al. 2004). On the early important displacement of the eastern flank of Etna. A morning of 28 October, the northern eruptive fissure survey on the summit of the volcano carried out imme- (N45–65E) propagated down-slope for 1.8 km to 1890 m a.s.l. The lower segment (3d, Fig. 3) of the fracture At about 4:00 GMT on 27 October, a third fissure opened along the NE-Rift. This fissure was 3.7 km long and trended SW-NE (Figs. 2, 4). It propagated between 2500 m and 1890 m a.s.l. in less than 24 h. In Fig. 3 we show segment 3a between 2500 and 2300 m a.s.l., trending N20–30E, that was 1.2 km long and showed violent strombolian activity. Segments 3b+3c of the fissure, 0.7 km long and trending N30–45E, formed in a right en-echelon arrangement between 2290 and 2190 m a.s.l., producing fire fountaining and effusive activity. Lava effusion produced a 1 km-long flow from a vent at 2500 m a.s.l. During the down-slope propagation of the fissure system a series of pit craters formed along the upper segments and the first, upper lava flow became inactive. Meanwhile, a second flow emerged from a vent at 2200 m a.s.l. flowing east and partially submerging the Piano Provenzana tourist infrastructure (Figs. 4, 6a). A shallow seismic swarm associated with the fissure propagation seriously damaged all of the tourist-hotel facilities on Piano Provenzana. The earthquakes caused movements along the whole PFS (~18 km) and up the Ionian coast (Acocella et al. 2003; Neri et al. 2004). On the early morning of 28 October, the northern eruptive fissure (N45–65E) propagated down-slope for 1.8 km to 1890 m a.s.l. The lower segment (3d, Fig. 3) of the fracture (~1 km long) showed continuous strombolian activity and a lava flow directed NE (Fig. 4), that travelled a distance of ~2.5 km (Fig. 6b) in a few hours. On 29 October, a NW-SE tectonic structure (SV in Fig. 1) located on the lower eastern flank of the volcano was activated by seismic swarms of 4.4 maximum mag- nitude that caused serious damage to houses and infrastructure around S. Venerina (SV in Fig. 1; Acocella et al. 2003). During the same day, the NE lava flow slowed and a new lava flow erupted from the same fissure (seg- ment 3d in Fig. 3) at 1930 m a.s.l., flowing SE and in- vading Piano Provenzana. The NE flow (Fig. 4) stopped on 31 October after having travelled 2.8 km, when a decline in effusion rate was observed. The explosive activity began to decrease slowly from 29 October and on 1 November it was limited to just two vents on the lower portion of the fissure, between 1950 and 1900 m a.s.l. This indicated a general waning of the eruptive activity on this side of the volcano. The eruptive plume did not exceed an altitude of 1 km above the vents, and fallout affected only the nearby areas. Strombolian activity formed two coalescent spatter cones at 1950–1900 m a.s.l. The E lava flow reached a final length of 6.2 km, and stopped its expansion on 3 November (Fig. 4). After lava supply from the main vent was cut off, 20 m of down- slope movement was observed at the most advanced flow front on 5 November. This late movement was caused by channel emptying, and occurred when lava coming from the main vent was completely crusted over. The ski station and tourist shops on Piano Provenzana were first destroyed by earthquakes then partially covered by lava flows. The flows also caused fires and destroyed parts of the old Linguaglossa pine forest (Fig. 4). Explosive and effusive activity completely stopped at the north fissure on 5 November. The morphology of the lava flows was “aa” in type, and the longer flows showed formation of wide ...

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... measurements of the relative amounts of SO 2 , HCl and HF in the volcanic plume emitted from Mt. Etna have been carried out since March 2000 with a Fourier transform infrared spectrometer (FTIR), using the sun as a source of radiation (Francis et al. 1998). Variations in the ratio of SO 2 /HCl are related to initial dissolved amounts for each species and to the degree of gas/magma separation that occurs during magma ascent within the volcanic edifice (Burton et al. 2003). During the 2002 eruption of Mt. Etna the SO 2 /HCl ratio of gases emitted from the explosive vent at 2750 m was measured regularly ( Fig. 8d). The first SO 2 /HCl ratio of 6.3 was measured on 28 October, after which the ratio decreased to 3 on 29 October before increasing at an approximately constant rate to 6 on 11 November, prior to a significant decrease to 3.5 on 12 November. This change was coincident with a temporary cessation of effusive activity, followed by a cyclic explosive activity that was measured contin- uously throughout the night of 12–13 November. After 12 November a strong increase in SO 2 /HCl ratio was observed from southern vent gas emissions, reaching a peak of 19 on 24 November, before declining and reaching a value of ~5 that was maintained until the end of the eruption with small variations. We believe that the variations observed during the first phase of activity (from 28 October to 12 November) were controlled primarily by the degree of gas/magma. A SO 2 /HCl ratio of 3 in the gas phase is consistent with complete equilibrium degassing of magma, suggesting that no gas/magma separation occurred, possibly assisted by magma fragmentation that strongly increased the surface area available for diffusion of volatiles from magma to the gas phase. As the eruption progressed, magma/gas separation began to become more important and became an increasingly significant factor in controlling the SO 2 /HCl ratio, primarily by inhibiting the diffusion of HCl into the gas phase either through accumulation of degassed magma at the conduit head or by less efficient fragmentation within the conduit. This was seen as an increasing SO 2 /HCl ratio between 30 October and 11 November that reached a critical point on 12 November when the amount of degassed magma in the conduit head was finally sufficient to inhibit fragmenta- tion, and the magma/gas mixture collapsed within the conduit for some hours, before gradually rising again, ex- hibiting strombolian and effusive activity. In order to understand if the 2002–03 southern flank activity showed uncommon volcanological features we compared it to past eruptions of Mt. Etna, examining in detail both eruptive style and intrusion dynamics. We were able to make this comparison for eruptions observed after 1700, when the location and timing of eruptive events started to be recorded and increasing scientific quality of the records allow us to define each event from a volcanological point of view (Branca and Del Carlo 2004). Searching the historical record for an eruption showing features similar to that of 2002–03, we find that during the last three centuries only one eruption, which occurred in the summer of 1763 (Recupero 1815), had similar characteristics to that of the 2002–03 S fissure. The 1763 eruption lasted 84 days, and started from an eruptive vent located very close to the area of the 2002-03 S fissure. It was characterised by intense and continuous explosive activity and by subordinate lava output that produced a 3.5 km-long lava flow. The explosive phase consisted of long periods of fire fountaining and minor strombolian activity that formed the La Montagnola scoria cone at 2500 m a.s.l. (Fig. 2). Fire fountain activity led to a few km-high eruptive columns, producing abundant lapilli and ash fallout on the SE flank down to Catania. The formation of a continuous lapilli and ash deposit caused considerable damage to cultivated areas. During the nineteenth century, several eruptions were characterised by strong explosive phases with lava effusion, such as the 1811, 1852–53, 1886 and 1892 eruptions. Vigorous explosive activity produced eruptive columns that caused an almost continuous tephra fall for a long period of time. During the twentieth century, no eruption showed similar explosive features compared to those of the nineteenth century. However, remarkable explosive activity occurred during the 2001 eruption (Calvari and INGV-CT 2001). This event was characterised by continuous explosive activity at the 2550 m vent, where a large scoria cone formed, and by effusive activity at the 2100 m vent that produced a 6.2 km-long lava flow field. Discontinuous ash emission from the 2550 m vent formed a 2–4 km-high sustained column. Lapilli and ash fell copiously for about ten days on the eastern flank of the volcano from Taormina to Catania (Fig. 1). In contrast, the 2002 eruptive activity along the NE-Rift showed the same explosive features and typical lava flow field evolution as the historical eruptions of this sector of the volcano (Branca and Del Carlo 2004). If we consider the composition of erupted products, the 2002–03 eruption showed the presence of two different magmas, as was the case in 2001 (Fig. 9). None of the historical eruptions of the last 300 years showed this double The multi-disciplinary and distinct magma approach output. to volcano In fact, monitoring although the at inant explosive activity, is comparable only with the eruptive Mt. Etna fissures allows opened evaluation in two of several different features areas of of the the La Montagnola 1763 and the 2001 Lower Vents eccentric volcano eruptive in dynamics 1879 and of 1949 the 2002–03 (Blaserna eruption, et al. 1879, and therefore Silvestri eruptions. Another unusual aspect is that the 2002–03 1879, allows Cumin us to determine 1950), forming in great a detail several the km-long evolution fissure of the eruption involved two simultaneous, independent lava system eruption. that Before dissected the onset the of summit the eruption, cone, these the presence eruptions of effusions showing different magma compositions and were magma connected in the upper to a single portion dike of intrusion the volcanic from edifice the central had styles of lava flow field emplacement. In this respect, the conduit been revealed feeding by system. several lines of evidence, such as: the NE-Rift system was fed by a hydrostatic supply of mag- renewal of strombolian activity at NEC, the increase in ma, whereas the S fissure was fed by discrete pulses of SO 2 flux at the summit craters, and development of hot magma. The NE fissure system followed the general trend cracks across the summit. Recently, Patan et al. (2003) of the NE-Rift eruptions, being characterised by a high argued that geodetic and seismic data recorded between effusion rate that rapidly declined, with long lava flows of 1994 and 2001 indicate a continuous injection of magma short duration. The S fissure system had a rather different from 6–15 km depth into the shallow (3–5 km) magma behaviour with short lava flows and effusion rate char- reservoir, with magma accumulation in the upper part of acterised by several short-term pulses and rather constant Mt. Etna’s plumbing system. Starting from these consid- peak values. Pulses in the magma supply rate were also erations, we propose two alternative hypotheses for the seen as pulses in the SO 2 flux. mechanism that triggered the rise of magma. (1) The ra- Anomalous features of the 2002–03 eruption are re- dial stress accompanying the deformation caused by mag- flected in petrological analyses. These indicate that two ma instrusion at 6–15 km depth caused the earthquake different magmas fed the NE and S fissure systems, as along the PFS on 22 September 2002. This could have occurred during the 2001 eruption. The 2001 and 2002–03 favoured the gradual upward magma movement and its eruptions represent the only cases of two distinct dike emergence on the surface about one month later. This is intrusions in the eruptive activity of the last 300 years at supported, on a local scale, by thermal camera monitoring Etna. In particular, petro-chemical features of the 2002– and field surveys which allowed the recognition of new 03 products strongly suggest the presence of a complex fractures in the summit area some months before the plumbing system (Fig. 12). Type 1 magma erupted from eruption onset. SO 2 flux measurements showed a slight the NE fissure represents the partially degassed resident increase from March 2002 onwards. (2) An alternative magma of the shallow plumbing system. Type 2 magma possibility is that depressurisation caused by active spread- erupted from the S fissure is an undegassed, volatile-rich, ing of Etna’s eastern flank may have triggered magma fast-rising magma that drains the deep portion of the output along the NE-Rift system (Acocella and Neri 2003, feeding system and bypasses the central conduits. The Acocella et al. 2003; Branca et al. 2003; Neri et al. 2004). synthesis of data from SO 2 gas flux, SO 2 /HCl gas ratio In fact, the eastern unstable area is bordered to the north and bulk rock CaO/Al 2 O 3 ratio (Fig. 8c) in tephra allows a by the E-W trending PFS. Data collected during the unique insight into the processes that controlled the initial 2002–03 eruption (Neri et al. 2004) indicate that: a) the stages of the 2002–03 Etna eruption. All three datasets fracture pattern along the PFS migrated from the NE Rift indicate that the first two days of the southern flank erup- east toward the coastline, nearly 20 km distant, and b) tion produced relatively fractionated magma. Data from then the deformation transferred along most of the ash analyses demonstrate that phreatomagmatic processes structures and faults on the eastern flank of Etna, migrated ...

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... two cameras. days of The the within changes the between upper part 3 and of 0 the (alternation feeder system of fire of fountains the volcano. and eruption first fixed showed video cracks camera formed was located by rapid at quenching, Milo (Fig. 1), and Additionally, strombolian activity) in several in a cases few hours, it was until possible the end to distin- of the thick 20.5 km vesicle distance walls from typical the of summit. uncompleted The second gas expan- video guish eruption the when SO 2 the flux expulsion emission of from ash eventually separate sources ceased. (N sion, camera and was many a mobile pyroclasts system were that coated has been by adhering located at dust the fissure, Summit Craters, and S fissure) that allowed in- (Andronico Serra La Nave et Observatory, al. 2003b). These 5 km from features, the fissure, in addition since to 4 vestigation of the magma supply rate to each eruptive the November higher lithic 2002 content, (Fig. 2). suggest The explosive an initial activity magma-water during vent. SO 2 flux in the plume of Mt. Etna has been routinely interaction the first month during of the the opening eruption phase has been of the analysed southern using fis- carried out using a COSPEC since 1987 (Caltabiano and sure. images During from most photographs, of the following videos and days, direct the observations juvenile ash Romano 1988; Caltabiano et al. 1994; Bruno et al. 1999, components taken during (tachylite, daily helicopter sideromelane flights. and Continuous loose crystals) video 2001). This long data set shows that SO 2 flux has a represented images were 100% not available of the total, during indicating this period that the due process to the background value of about 5300 t/d (metric tons per day) of damage magma caused fragmentation by the S. during Venerina the eruption earthquake was on pro- 29 during non-eruptive periods. After the 2001 flank erup- duced October mostly 2002. by exsolution and expansion of magmatic tion, SO 2 flux from summit craters showed atypical be- gases. We have estimated the intensity of ash emission using haviour, with values below 1000 t/d for ~15 months. This a qualitative observation of the density and height of the represented the longest continuous period of low SO 2 flux ash column, taking into account the wind speed and di- observed at Etna since 1987. This low rate of degassing rection. We divided the observed ash intensity into four could have been caused by a reduced magma supply to levels, ranging from 0 for no ash emission to 3 for the the upper part of the main feeder system of the volcano maximum intensity of ash emission during the eruption. (Salerno et al. 2003). A slightly increasing trend in the We have assigned a value of 1 to an ash emission in- SO 2 flux was observed beginning mid-March 2002, which tensity corresponding to 25% of the maximum intensity, coincided with the resumption of eruptive activity first at and value of 2 to 25–75% of the maximum intensity. NEC and then at BN, suggesting a slow increase in the These data have been plotted in Fig. 8a, and show a efficiency of convective mechanisms of the magma in the general decreasing trend, with several variations in in- upper part of the main feeder system of the volcano. On tensity during the eruption. In particular, from 27 October 25 October 2002, the SO 2 flux increased abruptly, coin- to 12 November, the activity was very stable and char- cident with the onset of the eruption, reaching a peak on acterised by high intensity of ash emission. Between 12 29 October. During the 2002–03 eruption, three main SO 2 and 14 November there was a sharp decrease in ash emission stages were identified (Fig. 8e), coinciding with emission due to a change from fire fountaining to mild changes in eruptive activity. strombolian explosions. From 14 to 25 November ash The period between 26 October and 14 November was emission exhibited some pulses. On 24 November it marked by the onset of the eruption and ended with a reached the value 0 due to the temporary cessation of significant SO 2 increase up to a peak on 14 November explosive activity at the 2750 m cone, which occurred just that correlated with changes in strombolian activity at the S fissure and the renewal of lava effusion. During this phase, the minimum SO 2 flux was recorded on 5 November, when lava effusion ceased at the N fissure. The period between 14 November and 28 November was characterised by a huge increase in SO 2 flux emission up to the highest value ever recorded at Mt. Etna (~29000 t/d, 28 November). This value occurred during Since 1994 a network of video cameras on the lower slopes of the volcano have provided a continuous view of the volcanic activity from different locations. In order to quantify the intensity of the explosive activity at the S fissure and its changes during the eruption, we have analysed the images recorded by two video cameras. The first fixed video camera was located at Milo (Fig. 1), 20.5 km distance from the summit. The second video camera was a mobile system that has been located at the Serra La Nave Observatory, 5 km from the fissure, since 4 November 2002 (Fig. 2). The explosive activity during the first month of the eruption has been analysed using images from photographs, videos and direct observations taken during daily helicopter flights. Continuous video images were not available during this period due to the damage caused by the S. Venerina earthquake on 29 October 2002. We have estimated the intensity of ash emission using a qualitative observation of the density and height of the ash column, taking into account the wind speed and direction. We divided the observed ash intensity into four levels, ranging from 0 for no ash emission to 3 for the maximum intensity of ash emission during the eruption. We have assigned a value of 1 to an ash emission intensity corresponding to 25% of the maximum intensity, and value of 2 to 25–75% of the maximum intensity. These data have been plotted in Fig. 8a, and show a general decreasing trend, with several variations in intensity during the eruption. In particular, from 27 October to 12 November, the activity was very stable and characterised by high intensity of ash emission. Between 12 and 14 November there was a sharp decrease in ash emission due to a change from fire fountaining to mild strombolian explosions. From 14 to 25 November ash emission exhibited some pulses. On 24 November it reached the value 0 due to the temporary cessation of explosive activity at the 2750 m cone, which occurred just the maximum explosive activity at the newly formed vent at 2800 m a.s.l. In contrast, the period between 28 November 2002 and 28 January 2003 was marked by a decrease in SO 2 emissions down to minimum values on December 2002, followed by a weak increase, which corresponded to a weak increase in eruptive activity at the S fissure. SO 2 flux oscillated, with the amplitude and period of these oscil- lations increasing over time. This behaviour, also seen in other Etnean eruptions, seems typical of the waning stage of an eruption, and preceded the end of this eruption on 28 January ...

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... vent. SO 2 flux in the plume of Mt. Etna has been routinely interaction the first month during of the the opening eruption phase has been of the analysed southern using fis- carried out using a COSPEC since 1987 (Caltabiano and sure. images During from most photographs, of the following videos and days, direct the observations juvenile ash Romano 1988; Caltabiano et al. 1994; Bruno et al. 1999, components taken during (tachylite, daily helicopter sideromelane flights. and Continuous loose crystals) video 2001). This long data set shows that SO 2 flux has a represented images were 100% not available of the total, during indicating this period that the due process to the background value of about 5300 t/d (metric tons per day) of damage magma caused fragmentation by the S. during Venerina the eruption earthquake was on pro- 29 during non-eruptive periods. After the 2001 flank erup- duced October mostly 2002. by exsolution and expansion of magmatic tion, SO 2 flux from summit craters showed atypical be- gases. We have estimated the intensity of ash emission using haviour, with values below 1000 t/d for ~15 months. This a qualitative observation of the density and height of the represented the longest continuous period of low SO 2 flux ash column, taking into account the wind speed and di- observed at Etna since 1987. This low rate of degassing rection. We divided the observed ash intensity into four could have been caused by a reduced magma supply to levels, ranging from 0 for no ash emission to 3 for the the upper part of the main feeder system of the volcano maximum intensity of ash emission during the eruption. (Salerno et al. 2003). A slightly increasing trend in the We have assigned a value of 1 to an ash emission in- SO 2 flux was observed beginning mid-March 2002, which tensity corresponding to 25% of the maximum intensity, coincided with the resumption of eruptive activity first at and value of 2 to 25–75% of the maximum intensity. NEC and then at BN, suggesting a slow increase in the These data have been plotted in Fig. 8a, and show a efficiency of convective mechanisms of the magma in the general decreasing trend, with several variations in in- upper part of the main feeder system of the volcano. On tensity during the eruption. In particular, from 27 October 25 October 2002, the SO 2 flux increased abruptly, coin- to 12 November, the activity was very stable and char- cident with the onset of the eruption, reaching a peak on acterised by high intensity of ash emission. Between 12 29 October. During the 2002–03 eruption, three main SO 2 and 14 November there was a sharp decrease in ash emission stages were identified (Fig. 8e), coinciding with emission due to a change from fire fountaining to mild changes in eruptive activity. strombolian explosions. From 14 to 25 November ash The period between 26 October and 14 November was emission exhibited some pulses. On 24 November it marked by the onset of the eruption and ended with a reached the value 0 due to the temporary cessation of significant SO 2 increase up to a peak on 14 November explosive activity at the 2750 m cone, which occurred just that correlated with changes in strombolian activity at the S fissure and the renewal of lava effusion. During this phase, the minimum SO 2 flux was recorded on 5 November, when lava effusion ceased at the N fissure. The period between 14 November and 28 November was characterised by a huge increase in SO 2 flux emission up to the highest value ever recorded at Mt. Etna (~29000 t/d, 28 November). This value occurred during clast Since component, 1994 a network whereas of video on 28 cameras October on this the lower value During before the the opening eruption, of daily two effusive measurements vents at of 2800 sulphur m. Be- di- dropped slopes of to the 9%. volcano Generally, have provided for the a entire continuous eruption, view the of oxide tween 26 (SO November 2 ) flux were and carried 10 December, out using ash emission a correlation was proportion the volcanic of activity lithics from in the different ash was locations. low, between In order 0 and to spectrometer intense and quite (COSPEC) stable, mounted with values on a between vehicle travelling 3 and 2. 3%, quantify with the values intensity of 13% of on the 13 explosive November activity and about at the 5% S underneath Finally, from the 10 plume. December The onwards analyses there of data was a collected general on fissure 12 December. and its changes Some during juvenile the clasts eruption, (tachylite we have and daily decrease provided in the essential intensity information of ash emission, on magma with behaviour sudden sideromelane) analysed the images ejected recorded during by the two first video two cameras. days of The the within changes the between upper part 3 and of 0 the (alternation feeder system of fire of fountains the volcano. and eruption first fixed showed video cracks camera formed was located by rapid at quenching, Milo (Fig. 1), and Additionally, strombolian activity) in several in a cases few hours, it was until possible the end to distin- of the thick 20.5 km vesicle distance walls from typical the of summit. uncompleted The second gas expan- video guish eruption the when SO 2 the flux expulsion emission of from ash eventually separate sources ceased. (N sion, camera and was many a mobile pyroclasts system were that coated has been by adhering located at dust the fissure, Summit Craters, and S fissure) that allowed in- (Andronico Serra La Nave et Observatory, al. 2003b). These 5 km from features, the fissure, in addition since to 4 vestigation of the magma supply rate to each eruptive the November higher lithic 2002 content, (Fig. 2). suggest The explosive an initial activity magma-water during vent. SO 2 flux in the plume of Mt. Etna has been routinely interaction the first month during of the the opening eruption phase has been of the analysed southern using fis- carried out using a COSPEC since 1987 (Caltabiano and sure. images During from most photographs, of the following videos and days, direct the observations juvenile ash Romano 1988; Caltabiano et al. 1994; Bruno et al. 1999, components taken during (tachylite, daily helicopter sideromelane flights. and Continuous loose crystals) video 2001). This long data set shows that SO 2 flux has a represented images were 100% not available of the total, during indicating this period that the due process to the background value of about 5300 t/d (metric tons per day) of damage magma caused fragmentation by the S. during Venerina the eruption earthquake was on pro- 29 during non-eruptive periods. After the 2001 flank erup- duced October mostly 2002. by exsolution and expansion of magmatic tion, SO 2 flux from summit craters showed atypical be- gases. We have estimated the intensity of ash emission using haviour, with values below 1000 t/d for ~15 months. This a qualitative observation of the density and height of the represented the longest continuous period of low SO 2 flux ash column, taking into account the wind speed and di- observed at Etna since 1987. This low rate of degassing rection. We divided the observed ash intensity into four could have been caused by a reduced magma supply to levels, ranging from 0 for no ash emission to 3 for the the upper part of the main feeder system of the volcano maximum intensity of ash emission during the eruption. (Salerno et al. 2003). A slightly increasing trend in the We have assigned a value of 1 to an ash emission in- SO 2 flux was observed beginning mid-March 2002, which tensity corresponding to 25% of the maximum intensity, coincided with the resumption of eruptive activity first at and value of 2 to 25–75% of the maximum intensity. NEC and then at BN, suggesting a slow increase in the These data have been plotted in Fig. 8a, and show a efficiency of convective mechanisms of the magma in the general decreasing trend, with several variations in in- upper part of the main feeder system of the volcano. On tensity during the eruption. In particular, from 27 October 25 October 2002, the SO 2 flux increased abruptly, coin- to 12 November, the activity was very stable and char- cident with the onset of the eruption, reaching a peak on acterised by high intensity of ash emission. Between 12 29 October. During the 2002–03 eruption, three main SO 2 and 14 November there was a sharp decrease in ash emission stages were identified (Fig. 8e), coinciding with emission due to a change from fire fountaining to mild changes in eruptive activity. strombolian explosions. From 14 to 25 November ash The period between 26 October and 14 November was emission exhibited some pulses. On 24 November it marked by the onset of the eruption and ended with a reached the value 0 due to the temporary cessation of significant SO 2 increase up to a peak on 14 November explosive activity at the 2750 m cone, which occurred just that correlated with changes in strombolian activity at the S fissure and the renewal of lava effusion. During this phase, the minimum SO 2 flux was recorded on 5 November, when lava effusion ceased at the N fissure. The period between 14 November and 28 November was characterised by a huge increase in SO 2 flux emission up to the highest value ever recorded at Mt. Etna (~29000 t/d, 28 November). This value occurred during Since 1994 a network of video cameras on the lower slopes of the volcano have provided a continuous view of the volcanic activity from different locations. In order to quantify the intensity of the explosive activity at the S fissure and its changes during the eruption, we have analysed the images recorded by two video cameras. The first fixed video camera was located at Milo (Fig. 1), 20.5 km distance from the summit. The second video camera was a mobile system that has been located at the Serra La Nave Observatory, 5 km from the fissure, since 4 November 2002 (Fig. 2). The explosive activity during the first ...

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... the eruption, daily measurements of sulphur di- oxide (SO 2 ) flux were carried out using a correlation spectrometer (COSPEC) mounted on a vehicle travelling underneath the plume. The analyses of data collected daily provided essential information on magma behaviour within the upper part of the feeder system of the volcano. Additionally, in several cases it was possible to distinguish the SO 2 flux emission from separate sources (N fissure, Summit Craters, and S fissure) that allowed in- vestigation of the magma supply rate to each eruptive vent. SO 2 flux in the plume of Mt. Etna has been routinely carried out using a COSPEC since 1987 (Caltabiano and Romano 1988; Caltabiano et al. 1994; Bruno et al. 1999, 2001). This long data set shows that SO 2 flux has a background value of about 5300 t/d (metric tons per day) during non-eruptive periods. After the 2001 flank eruption, SO 2 flux from summit craters showed atypical behaviour, with values below 1000 t/d for ~15 months. This represented the longest continuous period of low SO 2 flux observed at Etna since 1987. This low rate of degassing could have been caused by a reduced magma supply to the upper part of the main feeder system of the volcano (Salerno et al. 2003). A slightly increasing trend in the SO 2 flux was observed beginning mid-March 2002, which coincided with the resumption of eruptive activity first at NEC and then at BN, suggesting a slow increase in the efficiency of convective mechanisms of the magma in the upper part of the main feeder system of the volcano. On 25 October 2002, the SO 2 flux increased abruptly, coincident with the onset of the eruption, reaching a peak on 29 October. During the 2002–03 eruption, three main SO 2 emission stages were identified ( Fig. 8e), coinciding with changes in eruptive activity. The period between 26 October and 14 November was marked by the onset of the eruption and ended with a significant SO 2 increase up to a peak on 14 November that correlated with changes in strombolian activity at the S fissure and the renewal of lava effusion. During this phase, the minimum SO 2 flux was recorded on 5 November, when lava effusion ceased at the N fissure. The period between 14 November and 28 November was characterised by a huge increase in SO 2 flux emission up to the highest value ever recorded at Mt. Etna (~29000 t/d, 28 November). This value occurred during clast Since component, 1994 a network whereas of video on 28 cameras October on this the lower value During before the the opening eruption, of daily two effusive measurements vents at of 2800 sulphur m. Be- di- dropped slopes of to the 9%. volcano Generally, have provided for the a entire continuous eruption, view the of oxide tween 26 (SO November 2 ) flux were and carried 10 December, out using ash emission a correlation was proportion the volcanic of activity lithics from in the different ash was locations. low, between In order 0 and to spectrometer intense and quite (COSPEC) stable, mounted with values on a between vehicle travelling 3 and 2. 3%, quantify with the values intensity of 13% of on the 13 explosive November activity and about at the 5% S underneath Finally, from the 10 plume. December The onwards analyses there of data was a collected general on fissure 12 December. and its changes Some during juvenile the clasts eruption, (tachylite we have and daily decrease provided in the essential intensity information of ash emission, on magma with behaviour sudden sideromelane) analysed the images ejected recorded during by the two first video two cameras. days of The the within changes the between upper part 3 and of 0 the (alternation feeder system of fire of fountains the volcano. and eruption first fixed showed video cracks camera formed was located by rapid at quenching, Milo (Fig. 1), and Additionally, strombolian activity) in several in a cases few hours, it was until possible the end to distin- of the thick 20.5 km vesicle distance walls from typical the of summit. uncompleted The second gas expan- video guish eruption the when SO 2 the flux expulsion emission of from ash eventually separate sources ceased. (N sion, camera and was many a mobile pyroclasts system were that coated has been by adhering located at dust the fissure, Summit Craters, and S fissure) that allowed in- (Andronico Serra La Nave et Observatory, al. 2003b). These 5 km from features, the fissure, in addition since to 4 vestigation of the magma supply rate to each eruptive the November higher lithic 2002 content, (Fig. 2). suggest The explosive an initial activity magma-water during vent. SO 2 flux in the plume of Mt. Etna has been routinely interaction the first month during of the the opening eruption phase has been of the analysed southern using fis- carried out using a COSPEC since 1987 (Caltabiano and sure. images During from most photographs, of the following videos and days, direct the observations juvenile ash Romano 1988; Caltabiano et al. 1994; Bruno et al. 1999, components taken during (tachylite, daily helicopter sideromelane flights. and Continuous loose crystals) video 2001). This long data set shows that SO 2 flux has a represented images were 100% not available of the total, during indicating this period that the due process to the background value of about 5300 t/d (metric tons per day) of damage magma caused fragmentation by the S. during Venerina the eruption earthquake was on pro- 29 during non-eruptive periods. After the 2001 flank erup- duced October mostly 2002. by exsolution and expansion of magmatic tion, SO 2 flux from summit craters showed atypical be- gases. We have estimated the intensity of ash emission using haviour, with values below 1000 t/d for ~15 months. This a qualitative observation of the density and height of the represented the longest continuous period of low SO 2 flux ash column, taking into account the wind speed and di- observed at Etna since 1987. This low rate of degassing rection. We divided the observed ash intensity into four could have been caused by a reduced magma supply to levels, ranging from 0 for no ash emission to 3 for the the upper part of the main feeder system of the volcano maximum intensity of ash emission during the eruption. (Salerno et al. 2003). A slightly increasing trend in the We have assigned a value of 1 to an ash emission in- SO 2 flux was observed beginning mid-March 2002, which tensity corresponding to 25% of the maximum intensity, coincided with the resumption of eruptive activity first at and value of 2 to 25–75% of the maximum intensity. NEC and then at BN, suggesting a slow increase in the These data have been plotted in Fig. 8a, and show a efficiency of convective mechanisms of the magma in the general decreasing trend, with several variations in in- upper part of the main feeder system of the volcano. On tensity during the eruption. In particular, from 27 October 25 October 2002, the SO 2 flux increased abruptly, coin- to 12 November, the activity was very stable and char- cident with the onset of the eruption, reaching a peak on acterised by high intensity of ash emission. Between 12 29 October. During the 2002–03 eruption, three main SO 2 and 14 November there was a sharp decrease in ash emission stages were identified (Fig. 8e), coinciding with emission due to a change from fire fountaining to mild changes in eruptive activity. strombolian explosions. From 14 to 25 November ash The period between 26 October and 14 November was emission exhibited some pulses. On 24 November it marked by the onset of the eruption and ended with a reached the value 0 due to the temporary cessation of significant SO 2 increase up to a peak on 14 November explosive activity at the 2750 m cone, which occurred just that correlated with changes in strombolian activity at the S fissure and the renewal of lava effusion. During this phase, the minimum SO 2 flux was recorded on 5 November, when lava effusion ceased at the N fissure. The period between 14 November and 28 November was characterised by a huge increase in SO 2 flux emission up to the highest value ever recorded at Mt. Etna (~29000 t/d, 28 November). This value occurred during clast Since component, 1994 a network whereas of video on 28 cameras October on this the lower value During before the the opening eruption, of daily two effusive measurements vents at of 2800 sulphur m. Be- di- dropped slopes of to the 9%. volcano Generally, have provided for the a entire continuous eruption, view the of oxide tween 26 (SO November 2 ) flux were and carried 10 December, out using ash emission a correlation was proportion the volcanic of activity lithics from in the different ash was locations. low, between In order 0 and to spectrometer intense and quite (COSPEC) stable, mounted with values on a ...

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... deformation; (5) tion. The eruption was triggered either by (i) accumulation thermal imaging surveys carried out from both ground and eventual ascent of magma from depth or (ii) depres- and helicopter to detect new fractures and intra-crater surisation of the edifice due to spreading of the eastern activity; (6) quantitative analyses of ash components; (7) flank of the volcano. The extraordinary explosivity makes petrology of ash fall-out, scoria and lava emitted dur- the 2002–03 eruption a unique event in the last 300 years, ing eruptive activity. The use of fixed cameras, stream- comparable only with La Montagnola 1763 and the 2001 ing images of the volcano from various perspectives di- Lower Vents eruptions. A notable feature of the eruption rectly to the web, has also significantly improved the was also the simultaneous effusion of lavas with different visual monitoring of the volcano. In this paper we pres- composition and emplacement features. Magma erupted ent the results of these techniques, integrated to under- from the NE fissure represented the partially degassed stand the dynamics and eruptive behaviour of the last magma fraction normally residing within the central con- eruption. duits and the shallow plumbing system. The magma that erupted from the S fissure was the relatively undegassed, volatile-rich, buoyant fraction which drained the deep feeding system, bypassing the central conduits. This is Mount Etna is a basaltic volcano 3300 m high and covers an area of 1250 km 2 in Eastern Sicily, Italy (Fig. 1). A multi-disciplinary approach to its surveillance system has been active since the 1980s. More recently, the monitoring system has been further diversified, with a number of different investigations being carried out on a regular basis. These include: (1) regular field surveys of intra-crater activity; (2) three measurements of SO 2 flux from the summit craters using a correlation spectrometer (COSPEC); (3) frequent measurements of the chemical composition of magmatic gas emissions using Fourier Transform Infrared Spectroscopy (FTIR); (4) structural surveys to analyse the pattern of brittle deformation; (5) thermal imaging surveys carried out from both ground and helicopter to detect new fractures and intra-crater activity; (6) quantitative analyses of ash components; (7) petrology of ash fall-out, scoria and lava emitted during eruptive activity. The use of fixed cameras, stream- ing images of the volcano from various perspectives di- rectly to the web, has also significantly improved the visual monitoring of the volcano. In this paper we present the results of these techniques, integrated to understand the dynamics and eruptive behaviour of the last eruption. After the 1991–93 flank eruption (Calvari et al. 1994), from opposite flanks of the volcano. The 2002–03 erup- activity at Mt. Etna was typified for several years by mild tion was characterised by moderate emission of lava, degassing, alternated with summit eruptive activity. This intense explosive activity, and abundant ash emission, consisted of lava flow emission, strombolian explosions which caused damage to agriculture, housing and the lo- and paroxysmal events (Coltelli et al. 1998, 2000a; Cal- cal economy. vari et al. 2002; Calvari and Pinkerton 2002; Harris and The 2002–03 eruption involved two distinct magma Neri 2002; Alparone et al. 2003) at the summit craters intrusion zones, the NE-Rift and the S-Rift (Fig. 1) (Ki- (Fig. 1). This period stopped on 17 July 2001, when effer 1975; McGuire and Pullen 1989). The NE-Rift ex- magma quickly rose upward (Calvari and INGV-CT tends for about 7 km from the summit craters down to 2001; Acocella and Neri 2003; Behncke and Neri 2003a; 1500 m a.s.l., consisting of a network of N to NE-striking Lanzafame et al. 2003), producing intense explosive and eruptive fissures closely spaced in an area about 1–2 km effusive activity from several vents on the south-east wide (Garduæo et al. 1997). The NE-Rift is linked east- flank of the volcano. Although relatively short, the 2001 ward with the Pernicana Fault System (PFS in Fig. 1), a eruption displayed some important features: a very in- complex E-W oriented transtensive tectonic structure that tense seismic swarm lasting about a week before the onset dissects the NE flank of the volcano (Azzaro et al. 1998; of the eruption, the opening of two main systems of Groppelli and Tibaldi 1999; Neri et al. 2004). The last eruptive fissures (Billi et al. 2003; Lanzafame et al. 2003), eruption occurred there, in 1947, when a system of each one characterised by magma with peculiar compo- fissures developed from the North-East Crater (NEC, sition and petrography (Calvari and INGV-CT 2001), ~3300 m elevation, Fig. 3) down to 2150 m altitude, conspicuous lava emission threatening inhabited and forming a 6 km-long lava flow field (Cumin 1947; Ponte tourist areas, and violent explosive activity that led to the 1948; Cucuzza Silvestri 1949). The S-Rift (Fig. 1) com- formation of a 100 m high cinder cone (Behncke and Neri prises eruptive fissures distributed over a wider area, 2003a; Calvari and Pinkerton 2004) near La Montagnola extending from the summit craters to S and SE down to cone (Fig. 2). 600–700 m a.s.l. One third of the fissures on this sector of After a 15 month pause in activity, lava began to erupt the volcano developed as a consequence of eruptive ac- again on 26 October 2002. A short seismic swarm (Patan tivity over the last 2 ka (Del Carlo and Branca 1998). The 2002) preceded the almost simultaneous magma output upper portion of the S-Rift has been the preferential site of magma intrusion during the twentieth century, as indicated by the high occurrence of flank eruptions when compared to other sectors of the volcano (Behncke and Neri 2003b; Branca and Del Carlo 2004). The 2002–03 eruption shares many features with the 2001 event: (1) involvement of the same eruptive area on the south flank (Fig. 2); (2) strongly explosive style and lava output dynamics; (3) distinct magma compositions from the upper and lower fissure systems. In detail, the 2001 lower vents and the 2002–03 southern flank eruptions show features typical of the Etnean eccentric eruptions. Eccentric is the definition (Rittmann 1965) used for those Etnean eruptions fed by magma which bypasses the central conduit. These eruptions are characterised by a high tephra/lava ratio with prevalent ash emission, and low to medium phenocrysts content (Porphyritic In- dex<20%), with mafic minerals prevalent (Armienti et al. 1988). Here we present results obtained using different volcanological techniques, illustrating a multi-disciplinary approach that allowed us to monitor the eruptive events, and thereby promptly inform Civil Protection and local authorities of the possible evolution of the eruption. We use these results here to assess the triggering and eruptive mechanisms that caused the 2002–03 eruption, and by comparing our data with the historical activity of the volcano we infer the possible eruptive behaviour of Mt. Etna in the near future. After the 1991–93 flank eruption (Calvari et al. 1994), activity at Mt. Etna was typified for several years by mild degassing, alternated with summit eruptive activity. This consisted of lava flow emission, strombolian explosions and paroxysmal events (Coltelli et al. 1998, 2000a; Calvari et al. 2002; Calvari and Pinkerton 2002; Harris and Neri 2002; Alparone et al. 2003) at the summit craters (Fig. 1). This period stopped on 17 July 2001, when magma quickly rose upward (Calvari and INGV-CT 2001; Acocella and Neri 2003; Behncke and Neri 2003a; Lanzafame et al. 2003), producing intense explosive and effusive activity from several vents on the south-east flank of the volcano. Although relatively short, the 2001 eruption displayed some important features: a very intense seismic swarm lasting about a week before the onset of the eruption, the opening of two main systems of eruptive fissures (Billi et al. 2003; Lanzafame et al. 2003), each one characterised by magma with peculiar composition and petrography (Calvari and INGV-CT 2001), conspicuous lava emission threatening inhabited and tourist areas, and violent explosive activity that led to the formation of a 100 m high cinder cone (Behncke and Neri 2003a; Calvari and Pinkerton 2004) near La Montagnola cone (Fig. 2). After a 15 month pause in activity, lava began to erupt again on 26 October 2002. A short seismic swarm (Patan 2002) preceded the almost simultaneous magma output The opening of a new fissure system across the summit area of the volcano was heralded several months in ad- vance by the development of a field of cracks between North-East Crater (NEC) and South-East Crater (SEC; Fig. 3) in February 2002 (Calvari et al. 2003). The cracks showed a sharp thermal signature that was revealed through routine monthly monitoring carried out by helicopter-borne thermal surveys. Apart from high-temper- ature fumaroles, the cracks did not show any activity, and after the July–August 2001 flank eruption, no eruptive activity occurred on Etna’s summit for several months. On 8 March 2002, ash emission was observed from Bocca Nuova (BN; Fig. 3). This continued until 14 March, when it was observed that the ash emission was caused by failure of the inner crater walls, forming land- slides within the crater. Ash emission from BN was particularly intense on 20 March, when ash was reported to have fallen for about an hour between Zafferana and Giarre, about 20 km away from the summit. Ash emission was discontinuous until 25 March. On 28 March the NEC showed the same kind of activity and between April and June 2002 deep, intermittent explosions of variable intensity occurred in the BN and NEC craters. During June 2002, the ash emission from BN and NEC was intense and became continuous at NEC on 14 June, with pulses of dark ash rising to 500 m above the crater rim. Microscope analysis showed that ash ...

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... of the volcano, with lava flow output and fire fountaining until 5 November. After this date, the eruption continued exclusively on the S flank, with continuous explosive activity and lava flows active between 13 November and 28 January 2003. Multi-disciplinary data collected during the eruption (petrology, analyses of ash components, gas geochemistry, field surveys, thermal mapping and structural surveys) allowed us to analyse the dynamics of the eruption. The eruption was triggered either by (i) accumulation and eventual ascent of magma from depth or (ii) depressurisation of the edifice due to spreading of the eastern flank of the volcano. The extraordinary explosivity makes the 2002–03 eruption a unique event in the last 300 years, comparable only with La Montagnola 1763 and the 2001 Lower Vents eruptions. A notable feature of the eruption was also the simultaneous effusion of lavas with different composition and emplacement features. Magma erupted from the NE fissure represented the partially degassed magma fraction normally residing within the central conduits and the shallow plumbing system. The magma that erupted from the S fissure was the relatively undegassed, volatile-rich, buoyant fraction which drained the deep feeding system, bypassing the central conduits. This is Abstract The 2002–03 Mt Etna flank eruption began on Mount typical Etna of most is a basaltic Etnean volcano eccentric 3300 eruptions. m high We and believe covers 26 October 2002 and finished on 28 January 2003, after an that area there of is 1250 a high km probability 2 in Eastern that Sicily, Mount Italy Etna (Fig. 1). has entered A three months of continuous explosive activity and dis- multi-disciplinary a new eruptive phase, approach with to magma its surveillance being supplied system to has a continuous lava flow output. The eruption involved the been deep reservoir active since independent the 1980s. from More the central recently, conduit, the moni- that opening of eruptive fissures on the NE and S flanks of the toring could periodically system has been produce further sufficient diversified, overpressure with a to number prop- volcano, with lava flow output and fire fountaining until 5 of agate different a dyke investigations to the surface being and carried generate out further on a regular flank November. After this date, the eruption continued exclu- basis. eruptions. These include: (1) regular field surveys of in- sively on the S flank, with continuous explosive activity tra-crater activity; (2) three measurements of SO 2 flux and lava flows active between 13 November and 28 Jan- from Keywords the summit Multi-disciplinary craters using study a correlation · Mount spectrometer Etna · uary 2003. Multi-disciplinary data collected during the (COSPEC); 2002–03 eruption (3) frequent · Eccentric measurements eruptions · of Flank the activity chemical · eruption (petrology, analyses of ash components, gas geo- composition Etna feeding of system magmatic · Volcanic gas processes emissions using Fourier chemistry, field surveys, thermal mapping and structural Transform Infrared Spectroscopy (FTIR); (4) structural surveys) allowed us to analyse the dynamics of the erup- surveys to analyse the pattern of brittle deformation; (5) tion. The eruption was triggered either by (i) accumulation thermal imaging surveys carried out from both ground and eventual ascent of magma from depth or (ii) depres- and helicopter to detect new fractures and intra-crater surisation of the edifice due to spreading of the eastern activity; (6) quantitative analyses of ash components; (7) flank of the volcano. The extraordinary explosivity makes petrology of ash fall-out, scoria and lava emitted dur- the 2002–03 eruption a unique event in the last 300 years, ing eruptive activity. The use of fixed cameras, stream- comparable only with La Montagnola 1763 and the 2001 ing images of the volcano from various perspectives di- Lower Vents eruptions. A notable feature of the eruption rectly to the web, has also significantly improved the was also the simultaneous effusion of lavas with different visual monitoring of the volcano. In this paper we pres- composition and emplacement features. Magma erupted ent the results of these techniques, integrated to under- from the NE fissure represented the partially degassed stand the dynamics and eruptive behaviour of the last magma fraction normally residing within the central con- eruption. duits and the shallow plumbing system. The magma that erupted from the S fissure was the relatively undegassed, volatile-rich, buoyant fraction which drained the deep feeding system, bypassing the central conduits. This is Abstract The 2002–03 Mt Etna flank eruption began on Mount typical Etna of most is a basaltic Etnean volcano eccentric 3300 eruptions. m high We and believe covers 26 October 2002 and finished on 28 January 2003, after an that area there of is 1250 a high km probability 2 in Eastern that Sicily, Mount Italy Etna (Fig. 1). has entered A three months of continuous explosive activity and dis- multi-disciplinary a new eruptive phase, approach with to magma its surveillance being supplied system to has a continuous lava flow output. The eruption involved the been deep reservoir active since independent the 1980s. from More the central recently, conduit, the moni- that opening of eruptive fissures on the NE and S flanks of the toring could periodically system has been produce further sufficient diversified, overpressure with a to number prop- volcano, with lava flow output and fire fountaining until 5 of agate different a dyke investigations to the surface being and carried generate out further on a regular flank November. After this date, the eruption continued exclu- basis. eruptions. These include: (1) regular field surveys of in- sively on the S flank, with continuous explosive activity tra-crater activity; (2) three measurements of SO 2 flux and lava flows active between 13 November and 28 Jan- from Keywords the summit Multi-disciplinary craters using study a correlation · Mount spectrometer Etna · uary 2003. Multi-disciplinary data collected during the (COSPEC); 2002–03 eruption (3) frequent · Eccentric measurements eruptions · of Flank the activity chemical · eruption (petrology, analyses of ash components, gas geo- composition Etna feeding of system magmatic · Volcanic gas processes emissions using Fourier chemistry, field surveys, thermal mapping and structural Transform Infrared Spectroscopy (FTIR); (4) structural surveys) allowed us to analyse the dynamics of the erup- surveys to analyse the pattern of brittle deformation; (5) tion. The eruption was triggered either by (i) accumulation thermal imaging surveys carried out from both ground and eventual ascent of magma from depth or (ii) depres- and helicopter to detect new fractures and intra-crater surisation of the edifice due to spreading of the eastern activity; (6) quantitative analyses of ash components; (7) flank of the volcano. The extraordinary explosivity makes petrology of ash fall-out, scoria and lava emitted dur- the 2002–03 eruption a unique event in the last 300 years, ing eruptive activity. The use of fixed cameras, stream- comparable only with La Montagnola 1763 and the 2001 ing images of the volcano from various perspectives di- Lower Vents eruptions. A notable feature of the eruption rectly to the web, has also significantly improved the was also the simultaneous effusion of lavas with different visual monitoring of the volcano. In this paper we pres- composition and emplacement features. Magma erupted ent the results of these techniques, integrated to under- from the NE fissure represented the partially degassed stand the dynamics and eruptive behaviour of the last magma fraction normally residing within the central con- eruption. duits and the shallow plumbing system. The magma that erupted from the S fissure was the relatively undegassed, volatile-rich, buoyant fraction which drained the deep feeding system, bypassing the central conduits. This is Mount Etna is a basaltic volcano 3300 m high and covers an area of 1250 km 2 in Eastern Sicily, Italy (Fig. 1). A multi-disciplinary approach to its surveillance system has been active since the 1980s. More recently, the monitoring system has been further diversified, with a number of different investigations being carried out on a regular basis. These include: (1) regular field surveys of intra-crater activity; (2) three measurements of SO 2 flux from the summit craters using a correlation spectrometer (COSPEC); (3) frequent measurements of the chemical composition of magmatic gas emissions using Fourier Transform Infrared Spectroscopy (FTIR); (4) structural surveys to analyse the pattern of brittle deformation; (5) thermal imaging surveys carried out from both ground and helicopter to detect new fractures and intra-crater activity; (6) quantitative analyses of ash components; (7) petrology of ash fall-out, scoria and lava emitted during eruptive activity. The use of fixed cameras, stream- ing images of the volcano from various perspectives di- rectly to the web, has also significantly improved the visual monitoring of the volcano. In this paper we present the results of these techniques, integrated to understand the dynamics and eruptive behaviour of the last eruption. After the 1991–93 flank eruption (Calvari et al. 1994), from opposite flanks of the volcano. The 2002–03 erup- activity at Mt. Etna was typified for several years by mild tion was characterised by moderate emission of lava, degassing, alternated with summit eruptive activity. This intense explosive activity, and abundant ash emission, consisted of lava flow emission, strombolian explosions which caused damage to agriculture, housing and the lo- and paroxysmal events (Coltelli et al. 1998, 2000a; Cal- cal economy. vari et al. 2002; Calvari and Pinkerton 2002; Harris and The 2002–03 eruption involved two distinct magma Neri ...

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... rectly to the web, has also significantly improved the visual monitoring of the volcano. In this paper we present the results of these techniques, integrated to understand the dynamics and eruptive behaviour of the last eruption. After the 1991–93 flank eruption (Calvari et al. 1994), from opposite flanks of the volcano. The 2002–03 erup- activity at Mt. Etna was typified for several years by mild tion was characterised by moderate emission of lava, degassing, alternated with summit eruptive activity. This intense explosive activity, and abundant ash emission, consisted of lava flow emission, strombolian explosions which caused damage to agriculture, housing and the lo- and paroxysmal events (Coltelli et al. 1998, 2000a; Cal- cal economy. vari et al. 2002; Calvari and Pinkerton 2002; Harris and The 2002–03 eruption involved two distinct magma Neri 2002; Alparone et al. 2003) at the summit craters intrusion zones, the NE-Rift and the S-Rift (Fig. 1) (Ki- (Fig. 1). This period stopped on 17 July 2001, when effer 1975; McGuire and Pullen 1989). The NE-Rift ex- magma quickly rose upward (Calvari and INGV-CT tends for about 7 km from the summit craters down to 2001; Acocella and Neri 2003; Behncke and Neri 2003a; 1500 m a.s.l., consisting of a network of N to NE-striking Lanzafame et al. 2003), producing intense explosive and eruptive fissures closely spaced in an area about 1–2 km effusive activity from several vents on the south-east wide (Garduæo et al. 1997). The NE-Rift is linked east- flank of the volcano. Although relatively short, the 2001 ward with the Pernicana Fault System (PFS in Fig. 1), a eruption displayed some important features: a very in- complex E-W oriented transtensive tectonic structure that tense seismic swarm lasting about a week before the onset dissects the NE flank of the volcano (Azzaro et al. 1998; of the eruption, the opening of two main systems of Groppelli and Tibaldi 1999; Neri et al. 2004). The last eruptive fissures (Billi et al. 2003; Lanzafame et al. 2003), eruption occurred there, in 1947, when a system of each one characterised by magma with peculiar compo- fissures developed from the North-East Crater (NEC, sition and petrography (Calvari and INGV-CT 2001), ~3300 m elevation, Fig. 3) down to 2150 m altitude, conspicuous lava emission threatening inhabited and forming a 6 km-long lava flow field (Cumin 1947; Ponte tourist areas, and violent explosive activity that led to the 1948; Cucuzza Silvestri 1949). The S-Rift (Fig. 1) com- formation of a 100 m high cinder cone (Behncke and Neri prises eruptive fissures distributed over a wider area, 2003a; Calvari and Pinkerton 2004) near La Montagnola extending from the summit craters to S and SE down to cone (Fig. 2). 600–700 m a.s.l. One third of the fissures on this sector of After a 15 month pause in activity, lava began to erupt the volcano developed as a consequence of eruptive ac- again on 26 October 2002. A short seismic swarm (Patan tivity over the last 2 ka (Del Carlo and Branca 1998). The 2002) preceded the almost simultaneous magma output upper portion of the S-Rift has been the preferential site of magma intrusion during the twentieth century, as indicated by the high occurrence of flank eruptions when compared to other sectors of the volcano (Behncke and Neri 2003b; Branca and Del Carlo 2004). The 2002–03 eruption shares many features with the 2001 event: (1) involvement of the same eruptive area on the south flank (Fig. 2); (2) strongly explosive style and lava output dynamics; (3) distinct magma compositions from the upper and lower fissure systems. In detail, the 2001 lower vents and the 2002–03 southern flank eruptions show features typical of the Etnean eccentric eruptions. Eccentric is the definition (Rittmann 1965) used for those Etnean eruptions fed by magma which bypasses the central conduit. These eruptions are characterised by a high tephra/lava ratio with prevalent ash emission, and low to medium phenocrysts content (Porphyritic In- dex<20%), with mafic minerals prevalent (Armienti et al. 1988). Here we present results obtained using different volcanological techniques, illustrating a multi-disciplinary approach that allowed us to monitor the eruptive events, and thereby promptly inform Civil Protection and local authorities of the possible evolution of the eruption. We use these results here to assess the triggering and eruptive mechanisms that caused the 2002–03 eruption, and by comparing our data with the historical activity of the volcano we infer the possible eruptive behaviour of Mt. Etna in the near future. After the 1991–93 flank eruption (Calvari et al. 1994), activity at Mt. Etna was typified for several years by mild degassing, alternated with summit eruptive activity. This consisted of lava flow emission, strombolian explosions and paroxysmal events (Coltelli et al. 1998, 2000a; Calvari et al. 2002; Calvari and Pinkerton 2002; Harris and Neri 2002; Alparone et al. 2003) at the summit craters (Fig. 1). This period stopped on 17 July 2001, when magma quickly rose upward (Calvari and INGV-CT 2001; Acocella and Neri 2003; Behncke and Neri 2003a; Lanzafame et al. 2003), producing intense explosive and effusive activity from several vents on the south-east flank of the volcano. Although relatively short, the 2001 eruption displayed some important features: a very intense seismic swarm lasting about a week before the onset of the eruption, the opening of two main systems of eruptive fissures (Billi et al. 2003; Lanzafame et al. 2003), each one characterised by magma with peculiar composition and petrography (Calvari and INGV-CT 2001), conspicuous lava emission threatening inhabited and tourist areas, and violent explosive activity that led to the formation of a 100 m high cinder cone (Behncke and Neri 2003a; Calvari and Pinkerton 2004) near La Montagnola cone (Fig. 2). After a 15 month pause in activity, lava began to erupt again on 26 October 2002. A short seismic swarm (Patan 2002) preceded the almost simultaneous magma output The opening of a new fissure system across the summit area of the volcano was heralded several months in ad- vance by the development of a field of cracks between North-East Crater (NEC) and South-East Crater (SEC; Fig. 3) in February 2002 (Calvari et al. 2003). The cracks showed a sharp thermal signature that was revealed through routine monthly monitoring carried out by helicopter-borne thermal surveys. Apart from high-temper- ature fumaroles, the cracks did not show any activity, and after the July–August 2001 flank eruption, no eruptive activity occurred on Etna’s summit for several months. On 8 March 2002, ash emission was observed from Bocca Nuova (BN; Fig. 3). This continued until 14 March, when it was observed that the ash emission was caused by failure of the inner crater walls, forming land- slides within the crater. Ash emission from BN was particularly intense on 20 March, when ash was reported to have fallen for about an hour between Zafferana and Giarre, about 20 km away from the summit. Ash emission was discontinuous until 25 March. On 28 March the NEC showed the same kind of activity and between April and June 2002 deep, intermittent explosions of variable intensity occurred in the BN and NEC craters. During June 2002, the ash emission from BN and NEC was intense and became continuous at NEC on 14 June, with pulses of dark ash rising to 500 m above the crater rim. Microscope analysis showed that ash emitted after 21 June 2002 contained a juvenile component. On 23 June a helicopter-borne thermal survey showed elevated tem- peratures inside the NEC, suggesting that magma was very close to the surface. This was confirmed by field diately after the earthquake revealed that no eruptive activity had occurred within the craters. On 26 October 2002 at 20:12 GMT, an earthquake swarm recorded by our seismic network (Patan 2002; Acocella et al. 2003) preceded and accompanied the formation of eruptive fissures over the S and NE flanks of the volcano (Fig. 3), marking the onset of the 2002–03 Etna eruption. A north-south, 1 km-long eruptive fissure opened on the upper southern flank of the volcano (2850–2600 m a.s.l.), between Torre del Filosofo and the old cable-car station partially destroyed during the 1983 eruption (Figs. 2, 3). The fissure produced 100–300 m high fire fountains that soon evolved into an ash column up to about 5 km a.s.l. that was blown south by the wind. Another north-south, 340 m-long eruptive fissure opened at the northern base of NEC (3010–2920 m a.s.l.; Figs. 2, 4), producing fire fountains that lasted ~0.5 h. During this period NEC, VOR and BN showed increasing levels of explosive activity, consisting of pulsating ash emissions and intense short-lived strombolian activity. This produced distinct ash plumes that merged together and joined those orig- inating from the NE and S fissures, forming a large composite plume and causing abundant ash fall on the S and SE flanks of the volcano (Fig. 5). Table 1 summarizes the eruption ...

Context 11

... a new eruptive phase, approach with to magma its surveillance being supplied system to has a continuous lava flow output. The eruption involved the been deep reservoir active since independent the 1980s. from More the central recently, conduit, the moni- that opening of eruptive fissures on the NE and S flanks of the toring could periodically system has been produce further sufficient diversified, overpressure with a to number prop- volcano, with lava flow output and fire fountaining until 5 of agate different a dyke investigations to the surface being and carried generate out further on a regular flank November. After this date, the eruption continued exclu- basis. eruptions. These include: (1) regular field surveys of in- sively on the S flank, with continuous explosive activity tra-crater activity; (2) three measurements of SO 2 flux and lava flows active between 13 November and 28 Jan- from Keywords the summit Multi-disciplinary craters using study a correlation · Mount spectrometer Etna · uary 2003. Multi-disciplinary data collected during the (COSPEC); 2002–03 eruption (3) frequent · Eccentric measurements eruptions · of Flank the activity chemical · eruption (petrology, analyses of ash components, gas geo- composition Etna feeding of system magmatic · Volcanic gas processes emissions using Fourier chemistry, field surveys, thermal mapping and structural Transform Infrared Spectroscopy (FTIR); (4) structural surveys) allowed us to analyse the dynamics of the erup- surveys to analyse the pattern of brittle deformation; (5) tion. The eruption was triggered either by (i) accumulation thermal imaging surveys carried out from both ground and eventual ascent of magma from depth or (ii) depres- and helicopter to detect new fractures and intra-crater surisation of the edifice due to spreading of the eastern activity; (6) quantitative analyses of ash components; (7) flank of the volcano. The extraordinary explosivity makes petrology of ash fall-out, scoria and lava emitted dur- the 2002–03 eruption a unique event in the last 300 years, ing eruptive activity. The use of fixed cameras, stream- comparable only with La Montagnola 1763 and the 2001 ing images of the volcano from various perspectives di- Lower Vents eruptions. A notable feature of the eruption rectly to the web, has also significantly improved the was also the simultaneous effusion of lavas with different visual monitoring of the volcano. In this paper we pres- composition and emplacement features. Magma erupted ent the results of these techniques, integrated to under- from the NE fissure represented the partially degassed stand the dynamics and eruptive behaviour of the last magma fraction normally residing within the central con- eruption. duits and the shallow plumbing system. The magma that erupted from the S fissure was the relatively undegassed, volatile-rich, buoyant fraction which drained the deep feeding system, bypassing the central conduits. This is Mount Etna is a basaltic volcano 3300 m high and covers an area of 1250 km 2 in Eastern Sicily, Italy (Fig. 1). A multi-disciplinary approach to its surveillance system has been active since the 1980s. More recently, the monitoring system has been further diversified, with a number of different investigations being carried out on a regular basis. These include: (1) regular field surveys of intra-crater activity; (2) three measurements of SO 2 flux from the summit craters using a correlation spectrometer (COSPEC); (3) frequent measurements of the chemical composition of magmatic gas emissions using Fourier Transform Infrared Spectroscopy (FTIR); (4) structural surveys to analyse the pattern of brittle deformation; (5) thermal imaging surveys carried out from both ground and helicopter to detect new fractures and intra-crater activity; (6) quantitative analyses of ash components; (7) petrology of ash fall-out, scoria and lava emitted during eruptive activity. The use of fixed cameras, stream- ing images of the volcano from various perspectives di- rectly to the web, has also significantly improved the visual monitoring of the volcano. In this paper we present the results of these techniques, integrated to understand the dynamics and eruptive behaviour of the last eruption. After the 1991–93 flank eruption (Calvari et al. 1994), from opposite flanks of the volcano. The 2002–03 erup- activity at Mt. Etna was typified for several years by mild tion was characterised by moderate emission of lava, degassing, alternated with summit eruptive activity. This intense explosive activity, and abundant ash emission, consisted of lava flow emission, strombolian explosions which caused damage to agriculture, housing and the lo- and paroxysmal events (Coltelli et al. 1998, 2000a; Cal- cal economy. vari et al. 2002; Calvari and Pinkerton 2002; Harris and The 2002–03 eruption involved two distinct magma Neri 2002; Alparone et al. 2003) at the summit craters intrusion zones, the NE-Rift and the S-Rift (Fig. 1) (Ki- (Fig. 1). This period stopped on 17 July 2001, when effer 1975; McGuire and Pullen 1989). The NE-Rift ex- magma quickly rose upward (Calvari and INGV-CT tends for about 7 km from the summit craters down to 2001; Acocella and Neri 2003; Behncke and Neri 2003a; 1500 m a.s.l., consisting of a network of N to NE-striking Lanzafame et al. 2003), producing intense explosive and eruptive fissures closely spaced in an area about 1–2 km effusive activity from several vents on the south-east wide (Garduæo et al. 1997). The NE-Rift is linked east- flank of the volcano. Although relatively short, the 2001 ward with the Pernicana Fault System (PFS in Fig. 1), a eruption displayed some important features: a very in- complex E-W oriented transtensive tectonic structure that tense seismic swarm lasting about a week before the onset dissects the NE flank of the volcano (Azzaro et al. 1998; of the eruption, the opening of two main systems of Groppelli and Tibaldi 1999; Neri et al. 2004). The last eruptive fissures (Billi et al. 2003; Lanzafame et al. 2003), eruption occurred there, in 1947, when a system of each one characterised by magma with peculiar compo- fissures developed from the North-East Crater (NEC, sition and petrography (Calvari and INGV-CT 2001), ~3300 m elevation, Fig. 3) down to 2150 m altitude, conspicuous lava emission threatening inhabited and forming a 6 km-long lava flow field (Cumin 1947; Ponte tourist areas, and violent explosive activity that led to the 1948; Cucuzza Silvestri 1949). The S-Rift (Fig. 1) com- formation of a 100 m high cinder cone (Behncke and Neri prises eruptive fissures distributed over a wider area, 2003a; Calvari and Pinkerton 2004) near La Montagnola extending from the summit craters to S and SE down to cone (Fig. 2). 600–700 m a.s.l. One third of the fissures on this sector of After a 15 month pause in activity, lava began to erupt the volcano developed as a consequence of eruptive ac- again on 26 October 2002. A short seismic swarm (Patan tivity over the last 2 ka (Del Carlo and Branca 1998). The 2002) preceded the almost simultaneous magma output upper portion of the S-Rift has been the preferential site of magma intrusion during the twentieth century, as indicated by the high occurrence of flank eruptions when compared to other sectors of the volcano (Behncke and Neri 2003b; Branca and Del Carlo 2004). The 2002–03 eruption shares many features with the 2001 event: (1) involvement of the same eruptive area on the south flank (Fig. 2); (2) strongly explosive style and lava output dynamics; (3) distinct magma compositions from the upper and lower fissure systems. In detail, the 2001 lower vents and the 2002–03 southern flank eruptions show features typical of the Etnean eccentric eruptions. Eccentric is the definition (Rittmann 1965) used for those Etnean eruptions fed by magma which bypasses the central conduit. These eruptions are characterised by a high tephra/lava ratio with prevalent ash emission, and low to medium phenocrysts content (Porphyritic In- dex<20%), with mafic minerals prevalent (Armienti et al. 1988). Here we present results obtained using different volcanological techniques, illustrating a multi-disciplinary approach that allowed us to monitor the eruptive events, and thereby promptly inform Civil Protection and local authorities of the possible evolution of the eruption. We use these results here to assess the triggering and eruptive mechanisms that caused the 2002–03 eruption, and by comparing our data with the historical activity of the volcano we infer the possible eruptive behaviour of Mt. Etna in the near future. After the 1991–93 flank eruption (Calvari et al. 1994), activity at Mt. Etna was typified for several years by mild degassing, alternated with summit eruptive activity. This consisted of lava flow emission, strombolian explosions and paroxysmal events (Coltelli et al. 1998, 2000a; Calvari et al. 2002; Calvari and Pinkerton 2002; Harris and Neri 2002; Alparone et al. 2003) at the summit craters (Fig. 1). This period stopped on 17 July 2001, when magma quickly rose upward (Calvari and INGV-CT 2001; Acocella and Neri 2003; Behncke and Neri 2003a; Lanzafame et al. 2003), producing intense explosive and effusive activity from several vents on the south-east flank of the volcano. Although relatively short, the 2001 eruption displayed some important features: a very intense seismic swarm lasting about a week before the onset of the eruption, the opening of two main systems of eruptive fissures (Billi et al. 2003; Lanzafame et al. 2003), each one characterised by magma with peculiar composition and petrography (Calvari and INGV-CT 2001), conspicuous lava emission threatening inhabited and tourist areas, and violent explosive activity that led to the formation of a 100 m high cinder cone (Behncke and Neri 2003a; Calvari and Pinkerton 2004) near La Montagnola cone (Fig. 2). After a 15 month pause in activity, lava began to erupt again on ...

Context 12

... continued exclu- basis. eruptions. These include: (1) regular field surveys of in- sively on the S flank, with continuous explosive activity tra-crater activity; (2) three measurements of SO 2 flux and lava flows active between 13 November and 28 Jan- from Keywords the summit Multi-disciplinary craters using study a correlation · Mount spectrometer Etna · uary 2003. Multi-disciplinary data collected during the (COSPEC); 2002–03 eruption (3) frequent · Eccentric measurements eruptions · of Flank the activity chemical · eruption (petrology, analyses of ash components, gas geo- composition Etna feeding of system magmatic · Volcanic gas processes emissions using Fourier chemistry, field surveys, thermal mapping and structural Transform Infrared Spectroscopy (FTIR); (4) structural surveys) allowed us to analyse the dynamics of the erup- surveys to analyse the pattern of brittle deformation; (5) tion. The eruption was triggered either by (i) accumulation thermal imaging surveys carried out from both ground and eventual ascent of magma from depth or (ii) depres- and helicopter to detect new fractures and intra-crater surisation of the edifice due to spreading of the eastern activity; (6) quantitative analyses of ash components; (7) flank of the volcano. The extraordinary explosivity makes petrology of ash fall-out, scoria and lava emitted dur- the 2002–03 eruption a unique event in the last 300 years, ing eruptive activity. The use of fixed cameras, stream- comparable only with La Montagnola 1763 and the 2001 ing images of the volcano from various perspectives di- Lower Vents eruptions. A notable feature of the eruption rectly to the web, has also significantly improved the was also the simultaneous effusion of lavas with different visual monitoring of the volcano. In this paper we pres- composition and emplacement features. Magma erupted ent the results of these techniques, integrated to under- from the NE fissure represented the partially degassed stand the dynamics and eruptive behaviour of the last magma fraction normally residing within the central con- eruption. duits and the shallow plumbing system. The magma that erupted from the S fissure was the relatively undegassed, volatile-rich, buoyant fraction which drained the deep feeding system, bypassing the central conduits. This is Mount Etna is a basaltic volcano 3300 m high and covers an area of 1250 km 2 in Eastern Sicily, Italy (Fig. 1). A multi-disciplinary approach to its surveillance system has been active since the 1980s. More recently, the monitoring system has been further diversified, with a number of different investigations being carried out on a regular basis. These include: (1) regular field surveys of intra-crater activity; (2) three measurements of SO 2 flux from the summit craters using a correlation spectrometer (COSPEC); (3) frequent measurements of the chemical composition of magmatic gas emissions using Fourier Transform Infrared Spectroscopy (FTIR); (4) structural surveys to analyse the pattern of brittle deformation; (5) thermal imaging surveys carried out from both ground and helicopter to detect new fractures and intra-crater activity; (6) quantitative analyses of ash components; (7) petrology of ash fall-out, scoria and lava emitted during eruptive activity. The use of fixed cameras, stream- ing images of the volcano from various perspectives di- rectly to the web, has also significantly improved the visual monitoring of the volcano. In this paper we present the results of these techniques, integrated to understand the dynamics and eruptive behaviour of the last eruption. After the 1991–93 flank eruption (Calvari et al. 1994), from opposite flanks of the volcano. The 2002–03 erup- activity at Mt. Etna was typified for several years by mild tion was characterised by moderate emission of lava, degassing, alternated with summit eruptive activity. This intense explosive activity, and abundant ash emission, consisted of lava flow emission, strombolian explosions which caused damage to agriculture, housing and the lo- and paroxysmal events (Coltelli et al. 1998, 2000a; Cal- cal economy. vari et al. 2002; Calvari and Pinkerton 2002; Harris and The 2002–03 eruption involved two distinct magma Neri 2002; Alparone et al. 2003) at the summit craters intrusion zones, the NE-Rift and the S-Rift (Fig. 1) (Ki- (Fig. 1). This period stopped on 17 July 2001, when effer 1975; McGuire and Pullen 1989). The NE-Rift ex- magma quickly rose upward (Calvari and INGV-CT tends for about 7 km from the summit craters down to 2001; Acocella and Neri 2003; Behncke and Neri 2003a; 1500 m a.s.l., consisting of a network of N to NE-striking Lanzafame et al. 2003), producing intense explosive and eruptive fissures closely spaced in an area about 1–2 km effusive activity from several vents on the south-east wide (Garduæo et al. 1997). The NE-Rift is linked east- flank of the volcano. Although relatively short, the 2001 ward with the Pernicana Fault System (PFS in Fig. 1), a eruption displayed some important features: a very in- complex E-W oriented transtensive tectonic structure that tense seismic swarm lasting about a week before the onset dissects the NE flank of the volcano (Azzaro et al. 1998; of the eruption, the opening of two main systems of Groppelli and Tibaldi 1999; Neri et al. 2004). The last eruptive fissures (Billi et al. 2003; Lanzafame et al. 2003), eruption occurred there, in 1947, when a system of each one characterised by magma with peculiar compo- fissures developed from the North-East Crater (NEC, sition and petrography (Calvari and INGV-CT 2001), ~3300 m elevation, Fig. 3) down to 2150 m altitude, conspicuous lava emission threatening inhabited and forming a 6 km-long lava flow field (Cumin 1947; Ponte tourist areas, and violent explosive activity that led to the 1948; Cucuzza Silvestri 1949). The S-Rift (Fig. 1) com- formation of a 100 m high cinder cone (Behncke and Neri prises eruptive fissures distributed over a wider area, 2003a; Calvari and Pinkerton 2004) near La Montagnola extending from the summit craters to S and SE down to cone (Fig. 2). 600–700 m a.s.l. One third of the fissures on this sector of After a 15 month pause in activity, lava began to erupt the volcano developed as a consequence of eruptive ac- again on 26 October 2002. A short seismic swarm (Patan tivity over the last 2 ka (Del Carlo and Branca 1998). The 2002) preceded the almost simultaneous magma output upper portion of the S-Rift has been the preferential site of magma intrusion during the twentieth century, as indicated by the high occurrence of flank eruptions when compared to other sectors of the volcano (Behncke and Neri 2003b; Branca and Del Carlo 2004). The 2002–03 eruption shares many features with the 2001 event: (1) involvement of the same eruptive area on the south flank (Fig. 2); (2) strongly explosive style and lava output dynamics; (3) distinct magma compositions from the upper and lower fissure systems. In detail, the 2001 lower vents and the 2002–03 southern flank eruptions show features typical of the Etnean eccentric eruptions. Eccentric is the definition (Rittmann 1965) used for those Etnean eruptions fed by magma which bypasses the central conduit. These eruptions are characterised by a high tephra/lava ratio with prevalent ash emission, and low to medium phenocrysts content (Porphyritic In- dex<20%), with mafic minerals prevalent (Armienti et al. 1988). Here we present results obtained using different volcanological techniques, illustrating a multi-disciplinary approach that allowed us to monitor the eruptive events, and thereby promptly inform Civil Protection and local authorities of the possible evolution of the eruption. We use these results here to assess the triggering and eruptive mechanisms that caused the 2002–03 eruption, and by comparing our data with the historical activity of the volcano we infer the possible eruptive behaviour of Mt. Etna in the near future. After the 1991–93 flank eruption (Calvari et al. 1994), activity at Mt. Etna was typified for several years by mild degassing, alternated with summit eruptive activity. This consisted of lava flow emission, strombolian explosions and paroxysmal events (Coltelli et al. 1998, 2000a; Calvari et al. 2002; Calvari and Pinkerton 2002; Harris and Neri 2002; Alparone et al. 2003) at the summit craters (Fig. 1). This period stopped on 17 July 2001, when magma quickly rose upward (Calvari and INGV-CT 2001; Acocella and Neri 2003; Behncke and Neri 2003a; Lanzafame et al. 2003), producing intense explosive and effusive activity from several vents on the south-east flank of the volcano. Although relatively short, the 2001 eruption displayed some important features: a very intense seismic swarm lasting about a week before the onset of the eruption, the opening of two main systems of eruptive fissures (Billi et al. 2003; Lanzafame et al. 2003), each one characterised by magma with peculiar composition and petrography (Calvari and INGV-CT 2001), conspicuous lava emission threatening inhabited and tourist areas, and violent explosive activity that led to the formation of a 100 m high cinder cone (Behncke and Neri 2003a; Calvari and Pinkerton 2004) near La Montagnola cone (Fig. 2). After a 15 month pause in activity, lava began to erupt again on 26 October 2002. A short seismic swarm (Patan 2002) preceded the almost simultaneous magma output The opening of a new fissure system across the summit area of the volcano was heralded several months in ad- vance by the development of a field of cracks between North-East Crater (NEC) and South-East Crater (SEC; Fig. 3) in February 2002 (Calvari et al. 2003). The cracks showed a sharp thermal signature that was revealed through routine monthly monitoring carried out by helicopter-borne thermal surveys. Apart from high-temper- ature fumaroles, the cracks did not show any activity, and after the July–August 2001 flank eruption, no eruptive activity ...

Context 13

... analyse the dynamics of the erup- surveys to analyse the pattern of brittle deformation; (5) tion. The eruption was triggered either by (i) accumulation thermal imaging surveys carried out from both ground and eventual ascent of magma from depth or (ii) depres- and helicopter to detect new fractures and intra-crater surisation of the edifice due to spreading of the eastern activity; (6) quantitative analyses of ash components; (7) flank of the volcano. The extraordinary explosivity makes petrology of ash fall-out, scoria and lava emitted dur- the 2002–03 eruption a unique event in the last 300 years, ing eruptive activity. The use of fixed cameras, stream- comparable only with La Montagnola 1763 and the 2001 ing images of the volcano from various perspectives di- Lower Vents eruptions. A notable feature of the eruption rectly to the web, has also significantly improved the was also the simultaneous effusion of lavas with different visual monitoring of the volcano. In this paper we pres- composition and emplacement features. Magma erupted ent the results of these techniques, integrated to under- from the NE fissure represented the partially degassed stand the dynamics and eruptive behaviour of the last magma fraction normally residing within the central con- eruption. duits and the shallow plumbing system. The magma that erupted from the S fissure was the relatively undegassed, volatile-rich, buoyant fraction which drained the deep feeding system, bypassing the central conduits. This is Abstract The 2002–03 Mt Etna flank eruption began on Mount typical Etna of most is a basaltic Etnean volcano eccentric 3300 eruptions. m high We and believe covers 26 October 2002 and finished on 28 January 2003, after an that area there of is 1250 a high km probability 2 in Eastern that Sicily, Mount Italy Etna (Fig. 1). has entered A three months of continuous explosive activity and dis- multi-disciplinary a new eruptive phase, approach with to magma its surveillance being supplied system to has a continuous lava flow output. The eruption involved the been deep reservoir active since independent the 1980s. from More the central recently, conduit, the moni- that opening of eruptive fissures on the NE and S flanks of the toring could periodically system has been produce further sufficient diversified, overpressure with a to number prop- volcano, with lava flow output and fire fountaining until 5 of agate different a dyke investigations to the surface being and carried generate out further on a regular flank November. After this date, the eruption continued exclu- basis. eruptions. These include: (1) regular field surveys of in- sively on the S flank, with continuous explosive activity tra-crater activity; (2) three measurements of SO 2 flux and lava flows active between 13 November and 28 Jan- from Keywords the summit Multi-disciplinary craters using study a correlation · Mount spectrometer Etna · uary 2003. Multi-disciplinary data collected during the (COSPEC); 2002–03 eruption (3) frequent · Eccentric measurements eruptions · of Flank the activity chemical · eruption (petrology, analyses of ash components, gas geo- composition Etna feeding of system magmatic · Volcanic gas processes emissions using Fourier chemistry, field surveys, thermal mapping and structural Transform Infrared Spectroscopy (FTIR); (4) structural surveys) allowed us to analyse the dynamics of the erup- surveys to analyse the pattern of brittle deformation; (5) tion. The eruption was triggered either by (i) accumulation thermal imaging surveys carried out from both ground and eventual ascent of magma from depth or (ii) depres- and helicopter to detect new fractures and intra-crater surisation of the edifice due to spreading of the eastern activity; (6) quantitative analyses of ash components; (7) flank of the volcano. The extraordinary explosivity makes petrology of ash fall-out, scoria and lava emitted dur- the 2002–03 eruption a unique event in the last 300 years, ing eruptive activity. The use of fixed cameras, stream- comparable only with La Montagnola 1763 and the 2001 ing images of the volcano from various perspectives di- Lower Vents eruptions. A notable feature of the eruption rectly to the web, has also significantly improved the was also the simultaneous effusion of lavas with different visual monitoring of the volcano. In this paper we pres- composition and emplacement features. Magma erupted ent the results of these techniques, integrated to under- from the NE fissure represented the partially degassed stand the dynamics and eruptive behaviour of the last magma fraction normally residing within the central con- eruption. duits and the shallow plumbing system. The magma that erupted from the S fissure was the relatively undegassed, volatile-rich, buoyant fraction which drained the deep feeding system, bypassing the central conduits. This is Mount Etna is a basaltic volcano 3300 m high and covers an area of 1250 km 2 in Eastern Sicily, Italy (Fig. 1). A multi-disciplinary approach to its surveillance system has been active since the 1980s. More recently, the monitoring system has been further diversified, with a number of different investigations being carried out on a regular basis. These include: (1) regular field surveys of intra-crater activity; (2) three measurements of SO 2 flux from the summit craters using a correlation spectrometer (COSPEC); (3) frequent measurements of the chemical composition of magmatic gas emissions using Fourier Transform Infrared Spectroscopy (FTIR); (4) structural surveys to analyse the pattern of brittle deformation; (5) thermal imaging surveys carried out from both ground and helicopter to detect new fractures and intra-crater activity; (6) quantitative analyses of ash components; (7) petrology of ash fall-out, scoria and lava emitted during eruptive activity. The use of fixed cameras, stream- ing images of the volcano from various perspectives di- rectly to the web, has also significantly improved the visual monitoring of the volcano. In this paper we present the results of these techniques, integrated to understand the dynamics and eruptive behaviour of the last eruption. After the 1991–93 flank eruption (Calvari et al. 1994), from opposite flanks of the volcano. The 2002–03 erup- activity at Mt. Etna was typified for several years by mild tion was characterised by moderate emission of lava, degassing, alternated with summit eruptive activity. This intense explosive activity, and abundant ash emission, consisted of lava flow emission, strombolian explosions which caused damage to agriculture, housing and the lo- and paroxysmal events (Coltelli et al. 1998, 2000a; Cal- cal economy. vari et al. 2002; Calvari and Pinkerton 2002; Harris and The 2002–03 eruption involved two distinct magma Neri 2002; Alparone et al. 2003) at the summit craters intrusion zones, the NE-Rift and the S-Rift (Fig. 1) (Ki- (Fig. 1). This period stopped on 17 July 2001, when effer 1975; McGuire and Pullen 1989). The NE-Rift ex- magma quickly rose upward (Calvari and INGV-CT tends for about 7 km from the summit craters down to 2001; Acocella and Neri 2003; Behncke and Neri 2003a; 1500 m a.s.l., consisting of a network of N to NE-striking Lanzafame et al. 2003), producing intense explosive and eruptive fissures closely spaced in an area about 1–2 km effusive activity from several vents on the south-east wide (Garduæo et al. 1997). The NE-Rift is linked east- flank of the volcano. Although relatively short, the 2001 ward with the Pernicana Fault System (PFS in Fig. 1), a eruption displayed some important features: a very in- complex E-W oriented transtensive tectonic structure that tense seismic swarm lasting about a week before the onset dissects the NE flank of the volcano (Azzaro et al. 1998; of the eruption, the opening of two main systems of Groppelli and Tibaldi 1999; Neri et al. 2004). The last eruptive fissures (Billi et al. 2003; Lanzafame et al. 2003), eruption occurred there, in 1947, when a system of each one characterised by magma with peculiar compo- fissures developed from the North-East Crater (NEC, sition and petrography (Calvari and INGV-CT 2001), ~3300 m elevation, Fig. 3) down to 2150 m altitude, conspicuous lava emission threatening inhabited and forming a 6 km-long lava flow field (Cumin 1947; Ponte tourist areas, and violent explosive activity that led to the 1948; Cucuzza Silvestri 1949). The S-Rift (Fig. 1) com- formation of a 100 m high cinder cone (Behncke and Neri prises eruptive fissures distributed over a wider area, 2003a; Calvari and Pinkerton 2004) near La Montagnola extending from the summit craters to S and SE down to cone (Fig. 2). 600–700 m a.s.l. One third of the fissures on this sector of After a 15 month pause in activity, lava began to erupt the volcano developed as a consequence of eruptive ac- again on 26 October 2002. A short seismic swarm (Patan tivity over the last 2 ka (Del Carlo and Branca 1998). The 2002) preceded the almost simultaneous magma output upper portion of the S-Rift has been the preferential site of magma intrusion during the twentieth century, as indicated by the high occurrence of flank eruptions when compared to other sectors of the volcano (Behncke and Neri 2003b; Branca and Del Carlo 2004). The 2002–03 eruption shares many features with the 2001 event: (1) involvement of the same eruptive area on the south flank (Fig. 2); (2) strongly explosive style and lava output dynamics; (3) distinct magma compositions from the upper and lower fissure systems. In detail, the 2001 lower vents and the 2002–03 southern flank eruptions show features typical of the Etnean eccentric eruptions. Eccentric is the definition (Rittmann 1965) used for those Etnean eruptions fed by magma which bypasses the central conduit. These eruptions are characterised by a high tephra/lava ratio with prevalent ash emission, and low to medium phenocrysts content (Porphyritic In- dex<20%), with mafic ...

Context 14

... The 2002–03 Mt Etna flank eruption began on 26 October 2002 and finished on 28 January 2003, after three months of continuous explosive activity and discontinuous lava flow output. The eruption involved the opening of eruptive fissures on the NE and S flanks of the volcano, with lava flow output and fire fountaining until 5 November. After this date, the eruption continued exclusively on the S flank, with continuous explosive activity and lava flows active between 13 November and 28 January 2003. Multi-disciplinary data collected during the eruption (petrology, analyses of ash components, gas geochemistry, field surveys, thermal mapping and structural surveys) allowed us to analyse the dynamics of the eruption. The eruption was triggered either by (i) accumulation and eventual ascent of magma from depth or (ii) depressurisation of the edifice due to spreading of the eastern flank of the volcano. The extraordinary explosivity makes the 2002–03 eruption a unique event in the last 300 years, comparable only with La Montagnola 1763 and the 2001 Lower Vents eruptions. A notable feature of the eruption was also the simultaneous effusion of lavas with different composition and emplacement features. Magma erupted from the NE fissure represented the partially degassed magma fraction normally residing within the central conduits and the shallow plumbing system. The magma that erupted from the S fissure was the relatively undegassed, volatile-rich, buoyant fraction which drained the deep feeding system, bypassing the central conduits. This is Abstract The 2002–03 Mt Etna flank eruption began on Mount typical Etna of most is a basaltic Etnean volcano eccentric 3300 eruptions. m high We and believe covers 26 October 2002 and finished on 28 January 2003, after an that area there of is 1250 a high km probability 2 in Eastern that Sicily, Mount Italy Etna (Fig. 1). has entered A three months of continuous explosive activity and dis- multi-disciplinary a new eruptive phase, approach with to magma its surveillance being supplied system to has a continuous lava flow output. The eruption involved the been deep reservoir active since independent the 1980s. from More the central recently, conduit, the moni- that opening of eruptive fissures on the NE and S flanks of the toring could periodically system has been produce further sufficient diversified, overpressure with a to number prop- volcano, with lava flow output and fire fountaining until 5 of agate different a dyke investigations to the surface being and carried generate out further on a regular flank November. After this date, the eruption continued exclu- basis. eruptions. These include: (1) regular field surveys of in- sively on the S flank, with continuous explosive activity tra-crater activity; (2) three measurements of SO 2 flux and lava flows active between 13 November and 28 Jan- from Keywords the summit Multi-disciplinary craters using study a correlation · Mount spectrometer Etna · uary 2003. Multi-disciplinary data collected during the (COSPEC); 2002–03 eruption (3) frequent · Eccentric measurements eruptions · of Flank the activity chemical · eruption (petrology, analyses of ash components, gas geo- composition Etna feeding of system magmatic · Volcanic gas processes emissions using Fourier chemistry, field surveys, thermal mapping and structural Transform Infrared Spectroscopy (FTIR); (4) structural surveys) allowed us to analyse the dynamics of the erup- surveys to analyse the pattern of brittle deformation; (5) tion. The eruption was triggered either by (i) accumulation thermal imaging surveys carried out from both ground and eventual ascent of magma from depth or (ii) depres- and helicopter to detect new fractures and intra-crater surisation of the edifice due to spreading of the eastern activity; (6) quantitative analyses of ash components; (7) flank of the volcano. The extraordinary explosivity makes petrology of ash fall-out, scoria and lava emitted dur- the 2002–03 eruption a unique event in the last 300 years, ing eruptive activity. The use of fixed cameras, stream- comparable only with La Montagnola 1763 and the 2001 ing images of the volcano from various perspectives di- Lower Vents eruptions. A notable feature of the eruption rectly to the web, has also significantly improved the was also the simultaneous effusion of lavas with different visual monitoring of the volcano. In this paper we pres- composition and emplacement features. Magma erupted ent the results of these techniques, integrated to under- from the NE fissure represented the partially degassed stand the dynamics and eruptive behaviour of the last magma fraction normally residing within the central con- eruption. duits and the shallow plumbing system. The magma that erupted from the S fissure was the relatively undegassed, volatile-rich, buoyant fraction which drained the deep feeding system, bypassing the central conduits. This is Abstract The 2002–03 Mt Etna flank eruption began on Mount typical Etna of most is a basaltic Etnean volcano eccentric 3300 eruptions. m high We and believe covers 26 October 2002 and finished on 28 January 2003, after an that area there of is 1250 a high km probability 2 in Eastern that Sicily, Mount Italy Etna (Fig. 1). has entered A three months of continuous explosive activity and dis- multi-disciplinary a new eruptive phase, approach with to magma its surveillance being supplied system to has a continuous lava flow output. The eruption involved the been deep reservoir active since independent the 1980s. from More the central recently, conduit, the moni- that opening of eruptive fissures on the NE and S flanks of the toring could periodically system has been produce further sufficient diversified, overpressure with a to number prop- volcano, with lava flow output and fire fountaining until 5 of agate different a dyke investigations to the surface being and carried generate out further on a regular flank November. After this date, the eruption continued exclu- basis. eruptions. These include: (1) regular field surveys of in- sively on the S flank, with continuous explosive activity tra-crater activity; (2) three measurements of SO 2 flux and lava flows active between 13 November and 28 Jan- from Keywords the summit Multi-disciplinary craters using study a correlation · Mount spectrometer Etna · uary 2003. Multi-disciplinary data collected during the (COSPEC); 2002–03 eruption (3) frequent · Eccentric measurements eruptions · of Flank the activity chemical · eruption (petrology, analyses of ash components, gas geo- composition Etna feeding of system magmatic · Volcanic gas processes emissions using Fourier chemistry, field surveys, thermal mapping and structural Transform Infrared Spectroscopy (FTIR); (4) structural surveys) allowed us to analyse the dynamics of the erup- surveys to analyse ...

Context 15

... eruptive phase, approach with to magma its surveillance being supplied system to has a continuous lava flow output. The eruption involved the been deep reservoir active since independent the 1980s. from More the central recently, conduit, the moni- that opening of eruptive fissures on the NE and S flanks of the toring could periodically system has been produce further sufficient diversified, overpressure with a to number prop- volcano, with lava flow output and fire fountaining until 5 of agate different a dyke investigations to the surface being and carried generate out further on a regular flank November. After this date, the eruption continued exclu- basis. eruptions. These include: (1) regular field surveys of in- sively on the S flank, with continuous explosive activity tra-crater activity; (2) three measurements of SO 2 flux and lava flows active between 13 November and 28 Jan- from Keywords the summit Multi-disciplinary craters using study a correlation · Mount spectrometer Etna · uary 2003. Multi-disciplinary data collected during the (COSPEC); 2002–03 eruption (3) frequent · Eccentric measurements eruptions · of Flank the activity chemical · eruption (petrology, analyses of ash components, gas geo- composition Etna feeding of system magmatic · Volcanic gas processes emissions using Fourier chemistry, field surveys, thermal mapping and structural Transform Infrared Spectroscopy (FTIR); (4) structural surveys) allowed us to analyse the dynamics of the erup- surveys to analyse the pattern of brittle deformation; (5) tion. The eruption was triggered either by (i) accumulation thermal imaging surveys carried out from both ground and eventual ascent of magma from depth or (ii) depres- and helicopter to detect new fractures and intra-crater surisation of the edifice due to spreading of the eastern activity; (6) quantitative analyses of ash components; (7) flank of the volcano. The extraordinary explosivity makes petrology of ash fall-out, scoria and lava emitted dur- the 2002–03 eruption a unique event in the last 300 years, ing eruptive activity. The use of fixed cameras, stream- comparable only with La Montagnola 1763 and the 2001 ing images of the volcano from various perspectives di- Lower Vents eruptions. A notable feature of the eruption rectly to the web, has also significantly improved the was also the simultaneous effusion of lavas with different visual monitoring of the volcano. In this paper we pres- composition and emplacement features. Magma erupted ent the results of these techniques, integrated to under- from the NE fissure represented the partially degassed stand the dynamics and eruptive behaviour of the last magma fraction normally residing within the central con- eruption. duits and the shallow plumbing system. The magma that erupted from the S fissure was the relatively undegassed, volatile-rich, buoyant fraction which drained the deep feeding system, bypassing the central conduits. This is Mount Etna is a basaltic volcano 3300 m high and covers an area of 1250 km 2 in Eastern Sicily, Italy (Fig. 1). A multi-disciplinary approach to its surveillance system has been active since the 1980s. More recently, the monitoring system has been further diversified, with a number of different investigations being carried out on a regular basis. These include: (1) regular field surveys of intra-crater activity; (2) three measurements of SO 2 flux from the summit craters using a correlation spectrometer (COSPEC); (3) frequent measurements of the chemical composition of magmatic gas emissions using Fourier Transform Infrared Spectroscopy (FTIR); (4) structural surveys to analyse the pattern of brittle deformation; (5) thermal imaging surveys carried out from both ground and helicopter to detect new fractures and intra-crater activity; (6) quantitative analyses of ash components; (7) petrology of ash fall-out, scoria and lava emitted during eruptive activity. The use of fixed cameras, stream- ing images of the volcano from various perspectives di- rectly to the web, has also significantly improved the visual monitoring of the volcano. In this paper we present the results of these techniques, integrated to understand the dynamics and eruptive behaviour of the last eruption. After the 1991–93 flank eruption (Calvari et al. 1994), from opposite flanks of the volcano. The 2002–03 erup- activity at Mt. Etna was typified for several years by mild tion was characterised by moderate emission of lava, degassing, alternated with summit eruptive activity. This intense explosive activity, and abundant ash emission, consisted of lava flow emission, strombolian explosions which caused damage to agriculture, housing and the lo- and paroxysmal events (Coltelli et al. 1998, 2000a; Cal- cal economy. vari et al. 2002; Calvari and Pinkerton 2002; Harris and The 2002–03 eruption involved two distinct magma Neri 2002; Alparone et al. 2003) at the summit craters intrusion zones, the NE-Rift and the S-Rift (Fig. 1) (Ki- (Fig. 1). This period stopped on 17 July 2001, when effer 1975; McGuire and Pullen 1989). The NE-Rift ex- magma quickly rose upward (Calvari and INGV-CT tends for about 7 km from the summit craters down to 2001; Acocella and Neri 2003; Behncke and Neri 2003a; 1500 m a.s.l., consisting of a network of N to NE-striking Lanzafame et al. 2003), producing intense explosive and eruptive fissures closely spaced in an area about 1–2 km effusive activity from several vents on the south-east wide (Garduæo et al. 1997). The NE-Rift is linked east- flank of the volcano. Although relatively short, the 2001 ward with the Pernicana Fault System (PFS in Fig. 1), a eruption displayed some important features: a very in- complex E-W oriented transtensive tectonic structure that tense seismic swarm lasting about a week before the onset dissects the NE flank of the volcano (Azzaro et al. 1998; of the eruption, the opening of two main systems of Groppelli and Tibaldi 1999; Neri et al. 2004). The last eruptive fissures (Billi et al. 2003; Lanzafame et al. 2003), eruption occurred there, in 1947, when a system of each one characterised by magma with peculiar compo- fissures developed from the North-East Crater (NEC, sition and petrography (Calvari and INGV-CT 2001), ~3300 m elevation, Fig. 3) down to 2150 m altitude, conspicuous lava emission threatening inhabited and forming a 6 km-long lava flow field (Cumin 1947; Ponte tourist areas, and violent explosive activity that led to the 1948; Cucuzza Silvestri 1949). The S-Rift (Fig. 1) com- formation of a 100 m high cinder cone (Behncke and Neri prises eruptive fissures distributed over a wider area, 2003a; Calvari and Pinkerton 2004) near La Montagnola extending from the summit craters to S and SE down to cone (Fig. 2). 600–700 m a.s.l. One third of the fissures on this sector of After a 15 month pause in activity, lava began to erupt the volcano developed as a consequence of eruptive ac- again on 26 October 2002. A short seismic swarm (Patan tivity over the last 2 ka (Del Carlo and Branca 1998). The 2002) preceded the almost simultaneous magma output upper portion of the S-Rift has been the preferential site of magma intrusion during the twentieth century, as indicated by the high occurrence of flank eruptions when compared to other sectors of the volcano (Behncke and Neri 2003b; Branca and Del Carlo 2004). The 2002–03 eruption shares many features with the 2001 event: (1) involvement of the same eruptive area on the south flank (Fig. 2); (2) strongly explosive style and lava output dynamics; (3) distinct magma compositions from the upper and lower fissure systems. In detail, the 2001 lower vents and the 2002–03 southern flank eruptions show features typical of the Etnean eccentric eruptions. Eccentric is the definition (Rittmann 1965) used for those Etnean eruptions fed by magma which bypasses the central conduit. These eruptions are characterised by a high tephra/lava ratio with prevalent ash emission, and low to medium phenocrysts content (Porphyritic In- dex<20%), with mafic minerals prevalent (Armienti et al. 1988). Here we present results obtained using different volcanological techniques, illustrating a multi-disciplinary approach that allowed us to monitor the eruptive events, and thereby promptly inform Civil Protection and local authorities of the possible evolution of the eruption. We use these results here to assess the triggering and eruptive mechanisms that caused the 2002–03 eruption, and by comparing our data with the historical activity of the volcano we infer the possible eruptive behaviour of Mt. Etna in the near future. After the 1991–93 flank eruption (Calvari et al. 1994), activity at Mt. Etna was typified for several years by mild degassing, alternated with summit eruptive activity. This consisted of lava flow emission, strombolian explosions and paroxysmal events (Coltelli et al. 1998, 2000a; Calvari et al. 2002; Calvari and Pinkerton 2002; Harris and Neri 2002; Alparone et al. 2003) at the summit craters (Fig. 1). This period stopped on 17 July 2001, when magma quickly rose upward (Calvari and INGV-CT 2001; Acocella and Neri 2003; Behncke and Neri 2003a; Lanzafame et al. 2003), producing intense explosive and effusive activity from several vents on the south-east flank of the volcano. Although relatively short, the 2001 eruption displayed some important features: a very intense seismic swarm lasting about a week before the onset of the eruption, the opening of two main systems of eruptive fissures (Billi et al. 2003; Lanzafame et al. 2003), each one characterised by magma with peculiar composition and petrography (Calvari and INGV-CT 2001), conspicuous lava emission threatening inhabited and tourist areas, and violent explosive activity that led to the formation of a 100 m high cinder cone (Behncke and Neri 2003a; Calvari and Pinkerton 2004) near La Montagnola cone (Fig. 2). After a 15 month pause in activity, lava began to erupt again on 26 October ...